symmetrix foundations student resource guide[1]

7/27/2019 Symmetrix Foundations Student Resource Guide[1]

1/50Copyright 2004 EMC Corporation. All Rights Reserved.

Symmetrix Foundations, 1

11

EMC Global Education 2004 EMC Corporation. All rights reserved. These materials may not be copied without EMC's written consent.

Symmetrix Foundations

Welcome to Symmetrix Foundations. EMC offers a full range of storage platforms, from the CLARiiON CX200 at the

low end to the unsurpassed DMX3000 at the high end. This training provides an architectural introduction to the

Symmetrix family of products. The focus will be on DMX, but prior generations of Symmetrix will also be discussed.

Copyright 2004 EMC Corporation. All rights reserved.

These materials may not be copied without EMC's written consent.

EMC believes the information in this publication is accurate as of its publication date. The information is subject to

change without notice.

THE INFORMATION IN THIS PUBLICATION IS PROVIDED AS IS. EMC CORPORATION MAKES NO

REPRESENTATIONS OR WARRANTIES OF ANY KIND WITH RESPECT TO THE INFORMATION IN THIS

PUBLICATION, AND SPECIFICALLY DISCLAIMS IMPLIED WARRANTIES OF MERCHANTABILITY OR

FITNESS FOR A PARTICULAR PURPOSE.

Use, copying, and distribution of any EMC software described in this publication requires an applicable software

license.




EMC Global Education 2004 EMC Corporation. All rights reserved. 22

Audio Portion of this Course

z The AUDIO portion of this course is supplemental to thematerial and is not a replacement for the student notes

accompanying this course.z EMC recommends downloading the Student Resource

Guide (from the Supporting Materials tab) and readingthe notes in their entirety.

The AUDIO portion of this course is supplemental to the material and is not a replacement for the student notes

accompanying this course.

EMC recommends downloading the Student Resource Guide from the Supporting Materials tab, and reading the notes

in their entirety.





EMC Technology Foundations

z EMC Technology Foundations (ETF) is a curriculum that presents

overviews of EMC products and technologies including:

Symmetrix and CLARiiON Storage Platforms and Software SAN, NAS and CAS Networked Storage Solutions

Advanced storage management software

z The EMC Technology portfolio consists of end-to-end services andplatforms designed to accelerate the implementation of InformationLifecycle Management (ILM)

z ILM uses EMC technologies to enable organizations to better, and morecost-effectively, manage and protect their data, and achieve regulatorycompliance. It improves the availability of their business information in away that connects its use to business goals and service levels

z This course represents one part of the ETF curriculum

Companies across all industries are constantly launching new business-critical applications turning information into

strategic corporate assets. Value to the bottom line for customers, suppliers, and partners is often directly related to

how easily this information can be shared across the enterprise and beyond.

Information Lifecycle Management (ILM) is a flexible information-centric strategy that includes automating the

process of connecting applications and servers in an organization to its companys information. ILM includes Direct

Attached Storage (DAS), Storage Area Network (SAN), Network Attached Storage (NAS), Content Addressed

Storage (CAS), and software for management and automated provisioning.

ILM facilitates the integration of SAN and NAS, extends the reach of enterprise storage, and delivers a common way

to manage, share, and protect information. It also takes advantage of todays network and channel technologies to

consolidate servers and storage, centralize backup, and manage the explosive growth of data.





Symmetrix Foundations

After completing this course, you will be able to:

z Describe the basic architecture of a Symmetrix

Integrated Cached Disk Array (ICDA)z Identify the front-end, back-end, cache, and physical

drive configurations of various Symmetrix models

z Explain how Symmetrix functionally handles I/Orequests from the host environment

z Illustrate the relationship between Symmetrix physicaldisk drives and Symmetrix Logical Volumes

z Identify the media protection options available on theSymmetrix

These are the learning objectives for this training. Please take a moment to read them.





Symmetrix Integrated Cached Disk Array

z Highest level of performanceand availability in the industry

z

Consolidation Capacities to Terabytes Vast host connectivity

SAN or NAS

z Advanced functionality Parallel processing

architecture

Intelligent prefetch

Auto cache destage

Dynamic mirror service policy

Multi-region internal memory Predictive failure analysis and

call home

Back-end optimization

z Enginuity OperatingEnvironment

Base services for dataintegrity, optimization,

security, and Quality ofService

Core services for datamobility, sharing, repurposing,and recovery

There are basically three categories of storage architectures: Cache Centric, Storage Processor centric, and JBOD (Just

a Bunch Of Disks). The Symmetrix falls under the category of cache centric storage and is an Integrated Caching Disk

Array.





Enginuity Operating Environment

z Enginuity OperatingEnvironment is the Symmetrix

software that:

Manages all operations

Ensures data integrity

Optimizes performance

z Enginuity is often referred toas the microcode

z Solutions Enabler providescommon API and CLIinterface for managingSymmetrix and the entire

storage infrastructure

z

EMC and ISV developmanagement softwaresupporting heterogeneousplatforms using SolutionsEnabler API and CLIs

Symmetrix Hardware

Enginuity Operating Environment

Solutions Enabler Management

Symmetrix Based Applications

Host Based Management Software

ISV Software

Before we get into the hardware, lets briefly introduce the software components, as most functionality is based in

software and supported by the hardware.

Enginuity is the operating environment for the Symmetrix storage systems. Enginuity manages all Symmetrix

operations, from monitoring and optimizing internal data flow, to ensuring the fastest response to the users requestsfor information, to protecting and replicating data. Enginuity is often referred to as the Microcode.

Solutions Enabler is storage management that provides a common access mechanism for managing multivendor

environments, including the Symmetrix, storage, switches, and host storage resources. It enables the creation of

powerful storage management applications that dont have to understand the management details of each piece within

an EMC users environment.

Solutions Enabler is a development initiative (that is, a program available to Integrated Software Vendors (ISVs) and

developers through the EMC Developers Program) and provides a set of storage application programming interfaces

(APIs) that shield the management applications from the details beneath. It provides a common set of interfaces to

manage all aspects of storage. With Solutions Enabler providing building blocks for integrating layered software

applications, ISVs and third-party software developers (through the EMC Developers Program), and EMC software

developers are given wide-scale access to Enginuity functionality.





Symmetrix Card Cage

48

96

384576

288

288

144

144

120

Maximum DiskDrives

32GB2228230

128GB444DMX1000P

64GB4448530

64GB4888830256GB888DMX 3000

256GB888DMX2000P

256GB8412DMX2000

128GB426DMX1000

64GB222DMX800

MaximumCache

MaximumCacheDirectors

MaximumBack EndDirectors

MaximumFront EndDirectors

Model

DMX3000DMX2000DMX1000DMX800

Though we logically divide the architecture of the Symmetrix into Front End, Back End, and Shared Global Memory,

physically, these director and memory cards reside side-by-side within the card cage of the Symmetrix. The DMX P

model is configured for maximum performance rather than connectivity.





DMX2000

Symmetrix Architecture is based on the concept of N + 1 redundancy (one more component than is necessary for

operation).

Continuous Operation even if failures occur to any major component:

Global Memory Director boards Environmental Control Card Channel Director boards Cooling Fan Modules

Disk Director boards Power modules

Disk drives Batteries

Communications Control Card Service Processor

Power Subsystem: The Symmetrix has a modular power subsystem featuring a redundant architecture that facilitates

field replacement without interruption. The Symmetrix power subsystem connects to two dedicated or isolated AC

power lines. If AC power fails on one AC line, the power subsystem automatically switches to the other AC line.

System Battery Backup: The Symmetrix backup battery subsystem maintains power to the entire system if AC power

is lost. The backup battery subsystem allows Symmetrix to remain online to the host system for one to three minutes

(set in IMPL.bin file) in the event of an AC power loss, allowing the directors to flush cache write data to the disk

devices. Symmetrix continually recharges the battery subsystem whenever it is under AC power. When a power failure

occurs, power switches immediately to the backup battery, and Symmetrix continues to operate normally. When the

battery timer window elapses, Symmetrix presents a busy status to prevent the attached hosts from initiating any new

I/O. The Symmetrix destages any write data still in cache to disk, spins down the disk devices, and retracts the heads

and powers down.

Symmetrix Emergency Power Off: The Symmetrix emergency power off sequence allows 20 seconds to destage

pending write data. When the EPO switch is set to off, Symmetrix immediately switches to battery backup, and

initiates writes of cache data. Data is written to the first available spare area on any devices available for write. The

director records that there are pending write operations to complete, and stores the location of all data that has been

temporarily redirected. When power is restored, all data is written to its proper volumes.





Cache Management

Data path through Symmetrix Data destaged from cache

There are three functional areas:

Global Memory - provides cache memory and link between independent front end and back end

Channel director - how the Symmetrix connects to the host (server) environment (multi-processor circuit

boards) Disk director- how the Symmetrix controls and manages its physical disk drives, referred to as Disk Directors or

Disk Adapters

Channel directors handle I/O request from the host, while disk directors manage access to disk drives. The channel

directors and disk directors share global memory. Cache is used for staging and destaging data between the host and

the disk drives. Data is stored in cache as write pending, and an acknowledgement of data receipt is returned to the

host. The disk directors will write the data from cache to disk at a later time. The cache directory contains information

on data location, which data is still in cache, and which data has been written to disk.





Direct Matrix Architecture

What differentiates the Symmetrix generations and models is the number, type, and speed of the various

processors, and the technology used to interconnect the front-end and back-end with cache.

The DMX Series system currently uses M5 memory boards. Each memory board has sixteen ports, one to eachdirector. Each region can sustain a data rate of 500MBs, 4 regions per card, so 2GB per card. If a director is

removed from a system, the usable bandwidth is not reduced. If a memory board is removed, the usable bandwidth

is dropped by 2GB/s. In addition to 8 ports to front end hosts, or backend disks (depending on board type), each

director also has 8 ports to memory, one to each of the memory boards. All four processors can connect

concurrently to four different memory boards. In a fully configured Symmetrix DMX2000/3000 system, each of

the eight director ports on the sixteen directors connects to one of the sixteen memory ports on each of the eight

global memory directors. These 128 individual point-to-point connections facilitate up to 128 concurrent global

memory operations in the system.





Symmetrix DMX Architecture

Separate Controland

CommunicationsMessage Matrix

Disks

Servers

Another major performance improvement with the DMX is the separate control and communications matrix that

enables communication between the directors, without consuming cache bandwidth. This becomes more apparent as

we talk about read and write operations and the information flow through the Symmetrix later in this training.





DMX Director Pairing

Directors are paired Processor to Processor using the 17 rule. This means mirrors will notbe placed across Directors

using the 17 rule (unless only 2 Directors are present). Paired directors provide redundant paths to dual ported disks,

and will not use the same Port Bypass Card (PBC) in order to maintain redundancy on the Port Bypass Card level. The

PBC acts as the hub for all the Fibre disk drives in the disk cage.





DMX: Dual-ported Disk and Redundant Directors

z Directors are always configured inpairs to facilitate secondary pathsto drives

z Each disk module has two fully

independent Fibre Channel portsz Drive port connects to the Director

by a separate loop Each port connects to different

Directors in the Director pair

Port bypass cards prevent aDirector failure or replacementfrom affecting the other driveson the loop

z Directors have four primary loopsfor normal drive communicationand four secondary loops toprovide alternate path if the otherdirector fails (based onperformance models)

Disk Director 1 Disk Director 16

P

S

P

S

P

S

P

S

S

P

S

P

S

P

S

P

P = Primary Connection to Drive

S= Secondary Connection for Redundancy

Symmetrix DMX back-end employs an arbitrated loop design and dual-ported disk drives. Here is an example of a

9 disk per loop configuration. Each drive connects to two Disk Directors through separate Fibre Channel loops. The

loops are configured in a star-hub topology with gated hub ports and bypass switches, that allow individual Fibre

Channel disk drives to be dynamically inserted or removed.





Back-end Director Pairing 9-drive loopDirector 1d

dA

c

b

aBA

B

A

B

A

B

B

B

A

A

BB

A

A

BB

d A

c

b

a A

B

A

B

A

B

B

B

A

A

B

A

A

Director 16d

16d

C0

1d

C1

16d

C2

1d

C3

16d

C4

1d

C5

16d

C6

1d

C7

16d

C8

PBC

PBC

Legend

Primary Connection Director 1d

Bypass Connection Director 1d

Primary Connection Director 16d

Bypass Connection Director 16d

The Port Bypass Card contains the switch elements and control functions to allow intelligent management of the two

FC-AL loops embedded in each disk cage midplane. There are two Port Bypass Cards per disk cage midplane. Each

disk cage midplane can support 36 FC drives.

Each Processor has two ports, each with devices in the Front, as well as in the Back, Disk Midplane. In the above slide,

we are showing only one port from Director 1d, and one port from Director 16d. Notice that each Director has the

potential to access all Drives in the loop (9-drive loop configuration in this example). Notice also that using the Port

Bypass Card, each director is currently accessing only a portion of the drives (Director 1d has 4 Drives; Director 16d

has 5 Drives).

These Directors will have an opposite configuration on their second port, which is connected to a different Port Bypass

Card and Disk Midplane. For example, Director 1d has 4 Drives in this Disk Midplane, and on its other port it will

have 5. Director 16d has 5 Drives in this Disk Midplane, and on its other port it will have 4. Director 1d and Director

16d will be paired in both the front and back Disk Midplanes (only one shown here). With no component failure, each

processor will manage 4 drives on one port and 5 Drives on the other. These reside in Front and Back Disk Midplanes

and are referred to as C and D Devices. If the processor on Director 1d fails, the processor on Director 16d will now

access all 9 Drives on this loop.





DMX800 Architectural Overview

SPE

Enclosure

The physical layout of the DMX800 is very different than previous Symmetrix models. Directors, Memory, back

adapter functionality, communications and environmental functions are all in the Storage Processor Enclosure

(SPE). The DMX800 looks similar to the CLARiiON CX600 series and does in fact use the same back end style

components.

The SPE Contains 2 - 4 Fibre director boards, up to 2 Multi Protocol Boards, 2 Memory boards, 2 Front-end Back-

end (FEBE) adapters, Redundant Power Supplies and Fan module.

The DMX800 does not contain disk drive cages; drives are in a separate Disk Array Enclosure (DAE). Each DAE

has 2 Link Controller Cards (LCCs) and 2 Power Supplies. The Service Processor is replaced by a 1U (1U = 1.75)

Server, the Server will support 4 SPEs via 4 of its 6 Ethernet connections.

Batteries, or Standby Power Supplies (SPS), are in a separate 1U enclosure. Each SPS enclosure contains two

SPSes, and supports either two DAEs or one SPE. There are no ECM or CCM boards in the DMX800. TheCommunication and Environmental functions are taken care of by Directors and FEBE Adapters.





Symmetrix 5.X LVD Architecture

80 MBS SCSI LVD Bus

Shared Global Memory Back EndFront End

Channel Director

Processor bPowerPC 750

333Mhz

Low Memory

Top High

Bottom Low Bottom High

Processor aPowerPC 750

333 Mhz

400 MBS

Internal

Bus

400 MBS

Internal

Bus

Top Low

High Memory

Cache

Disk Director

Processor bPowerPC 750

333Mhz

Processor aPowerPC 750

333 Mhz

8230 BayCabinet

8530

8830

1 BayCabinet

3 BayCabinet

Here is another example of the MOSAIC 2000 Architecture. This is the basic architecture for Symmetrix 5.X LVD:

Bus speed of 400MB/s for an aggregate of 1600 MB/s

Back End Directors and Drives support Ultra 2 SCSI LVD (Low Voltage Differential) and the bus speed of 80

MB/s The director processors are now 333 Mhz; ESCON directors are 400 Mhz

Each director connects to 2 internal system buses (Top High & Bottom Low for odd directors | Bottom High &

Top Low for even directors )

M4 Generation of Memory Boards support LVD ( Low Voltage Differential or Ultra 2 SCSI Enginuity 5567 or

greater)

The Symmetrix 5 (8730, 8430) follows the same bus structure but has speeds of 360MB/s for an aggregate of 1440

MB/s.

The Symmetrix 4.X family is based on a dual system bus design. Each director is connected to either the X bus (odd

numbered director) or Y bus (even numbered director). Each director card has two sides, the bprocessor (top half)

and the aprocessor (bottom half). Data is transferred throughout the Symmetrix (from Channel Director to Memory to

Disk Director) in a serial fashion along the system buses. For every 64 bits of data, the Symmetrix creates a 72 bit

Memory Word (64 bits of data + 8 bits of parity). These Memory Words are then sent in a serial fashion across the

internal buses to director from cache or to cache from director.





DA 2

Processor b

MIDPLANE

DA 1

Processor b

MIDPLANE

Port D

Port C

Port D

Port C

Solid line = Primary Path

Dotted line = Secondary Path

Symm 5: Dual-Initiator Disk Director

z Disk Directors are installed inpairs to facilitate secondarypaths to drives

z In the unlikely event of a disk

director processor failure, theadjacent director will continueservicing the attached drivesthrough secondary path In this example, DA1

processor b would see portsC & D for DA2 processor bas its A & B ports in a fail-overscenario

z Protecting against DAprocessor card failure

z

Physical drives are not dual-ported but are connected via adual-initiator SCSI Bus

z Volumes are typically mirroredacross directors

Symmetrix 4 and 5 architectures utilize a dual-initiator back-end architecture that ensures continuous availability of

data in the unlikely event of a Disk Director failure. This feature works by having two disk directors shadow the

function of each other. That is, each disk director has the capability of servicing any or all of the disk devices of the

disk director it is paired with. Under normal conditions, each disk director only services its disk devices. If Symmetrix

detects a disk director hardware failure, Symmetrix calls home but continues to read from or write to the disk

devices through the disk director it is paired with. When the source of the failure is corrected, Symmetrix returns the

I/O servicing of the two disk directors to their normal state.

Prior to the Symmetrix DMX, mirrored volumes were configured with what is known as the rule of 17. Because of

where within the card cage the DA pairs reside (1/2, 3/4, 13/14, 15/16), as long as the sum of the DA director numbers

equals 17 (1/16, 2/15, 3/14, 4/13), the mirrors will always be on different internal system buses and dual initiators for

the highest availability and maximum Symmetrix resources.

Note: On the 4.x family, dual-initiation occurs by physically connecting one disk directors port card to the port card of

the adjacent disk director with a dual slotted adapter card.





Symmetrix Back End

z Symmetrix 4 and 5architectures use 40/80MB/sSCSI to connect physical

drives with a maximum of 12drives per port

z DAs installed in pairs onadjacent slots within the cardcage of Symmetrix

z DMX Architecture uses 2GbFibre Channel drives

Eight ports per Director

Maximum 18 dual porteddrives per port

Port C

Port D

Port C

Port D

Disk Director

Processor b

Processor a

dA

c

b

aBA

B

A

B

AB

BB

A

A

BB

AA

The primary purpose of the Back End director is to read and write data to the physical disks. However, when it is not

staging data in cache or destaging data to disk, the disk director is responsible for proactive monitoring of physical

drives and cache memory. This is referred to as disk and cache scrubbing.

Disk Scrubbing or Disk Error Correction and Error Verification: The disk directors use idle time to read data and

check the polynomial correction bits for validity. If a disk read error occurs, the disk director reads all data on that

track to Symmetrix cache memory. The disk director writes several worst case patterns to that track searching for

media errors. When the test completes, the disk director rewrites the data from cache to the disk device, verifying the

write operation. The disk microprocessor maps around any bad block (or blocks) detected during the worst case write

operation, thus skipping defects in the media. When the internal soft error threshold is reached, the Symmetrix service

processor automatically dials the EMC Customer Support Center and notifies the host system of errors via sense data.

Cache Scrubbing or Cache Error Correction and Error Verification: The disk directors use idle time to periodically

read cache, correct errors, and write the corrected data back to cache. This process is called error verification or

scrubbing. When the directors detect an uncorrectable error in cache, Symmetrix reads the data from disk and takes

the defective cache memory block offline until an EMC Customer Engineer can repair it. Error verification maximizesdata availability by significantly reducing the probability of encountering an uncorrectable error by preventing bit

errors from accumulating in cache.





Symmetrix Global Cache Directors

z Memory boards are now referredto as Global Cache Directorsand contain global shared

memoryz Boards are comprised of memory

chips and divided into fouraddressable regions

z Symmetrix has a minimum of 2memory boards and a maximumof 8. Generally installed in pairs

z Individual cache directors areavailable in 2 GB, 4 GB, 8 GB,16 GB and 32 GB sizes

z Memory boards are FRUs andhot swappable (does not requireSymmetrix power down orreboot)

Cache boards are designed for each family of Symmetrix. Symmetrix 4.8 uses the M2 generation of memory boards

that connect to both the X and Y internal buses. Symmetrix 5 uses the M3/M4 generation of memory boards and the

DMX uses M5. Because these boards have different designs, they cannot be swapped between families of Symmetrix.

On Symmetrix 5, memory boards that connect to the Top High and Bottom High internal system buses are referred to

as High Memory. Conversely, boards that connect to Top Low and Bottom Low are known as Low Memory.

DMX uses direct connections between directors and cache.

When configuring cache for the Symmetrix DMX systems, follow these guidelines:

A minimum of four and a maximum of eight cache director boards is required for the DMX2000 and DMX3000

system configuration; and a minimum of two and a maximum of four cache director boards is required for the

DMX1000 system configuration.

Two-board cache director configurations require boards of equal size.

Cache directors can be added one at a time to configurations of two boards and greater.

A maximum of two different cache director sizes is supported, and the smallest cache director must be at leastone-half the size of the largest cache director.

In cache director configurations with more than two boards, no more than one half of the boards can be smaller

than the largest cache director.





Cache Age Link Chain

z Locality of Reference If a data block has been recently

used, adjacent data will be

needed soon Prefetch algorithm detects

sequential data access patterns

z Data Re-use Accessed Data will probably be

used again

z Least Recently Used Flush old data from cache and

only keep active data in cache

Free up cache slots that are

inactive to make room for moreactive data

Cache is allocated in tracks referred to as cache slots, which are 32Kbytes in size (57 Kbytes for Mainframe). If the

Symmetrix is supporting both FBA and CKD emulation within the same frame, the cache slots will equal the largest

track size, 57K (3390). The Track Table is a directory of the data residing in cache and of the location/condition of the

data residing on Symmetrix physical disk(s). Track Tables are used to keep the status of each track, and of each logical

volume. Approximately 16 Bytes of cache space is used for each track.

Prefetching is done by the Disk Director. Once sequential access is detected, prefetch is automatically turned on for

that logical volume. Prefetch is initiated by 2 sequential accesses to a volume. Once turned on, for every sequential

access, the Symmetrix will pull the next two successive tracks into cache (access to track 1 on cylinder 1 and will

prompt the prefetch of tracks 2 & 3 on cylinder 1). After 100 sequential accesses to that volume, the next sequential

access will initiate the prefetching of the next 5 tracks on that volume (access to track 1 on cylinder 10 will prompt the

prefetch of tracks 2, 3, 4, 5 & 6 on cylinder 10). After the next 100 sequential accesses to that volume, the prefetch

track value is increased to 8 (access to track 1 on cylinder 100 will prompt the prefetch of tracks 2, 3, 4, 5, 6, 7, 8 & 9

on cylinder 100). Any non-sequential accesses to that volume will turn the prefetch capability off.

As data is placed into cache or accessed within cache, it is given a pseudo timestamp. This allows the Symmetrix tomaintain only the most frequently accessed data in cache memory. The data residing in cache is ordered through an

Age-Link-Chain. As data is touched (read operation for example), it moves to the top of the Age-Link-Chain. Every

time a director performs a cache operation, it must take control of the LRU algorithm. This forces the director to mark

the least recently used data in cache to be overwritten by the next cache operation.





Read Operations

Read Hit

In a read hit operation, the requested data resides in global memory. The channel director transfers the requested datathrough the channel interface to the host, and updates the global memory director. Since the data is in global memory,there are no mechanical delays due to seek, latency, and rotational position sensing that is encountered with disk.

Read Miss

In a read miss operation, the requested data is not in global memory, and must be retrieved from a disk device. Thedisk director stores the data in global memory and updates the directory table. The Channel director then reconnectswith the host and transfers the data. The host sends an acknowledgement and the directory tables are updated.





Write Operations

Fast Write

On a write command, the channel director places the incoming blocks directly into global memory. The channel

director sends an acknowledgement to the host. The directory tables are updated, and the disk director will

asynchronously destage the data from global memory to the disk device.

Delayed fast Write

A delayed fast write occurs only when the fast write threshold has been exceeded. That is, the percentage of global

memory containing modified data is higher than the fast write threshold. If this situation occurs, the Symmetrix system

disconnects the channel director(s) from the channel. The disk directors then destage the Least Recently Used data to

disk. When sufficient global memory space is available, the channel directors reconnect to their channels, and process

the host I/O request as a fast write. The Symmetrix system continues to process read operations during delayed fast

writes. With sufficient global memory present, this type of global memory operation rarely occurs.





Cache Allocation

z Cache algorithms are designed to optimize cache utilization andfairness for all Symmetrix Volumes

z Cache allocation dynamically adjust based on current usage Symmetrix constantly monitors system utilization (including individual

volume activity)

More active volumes are dynamically allocated additional cacheresources from relatively less active volumes

Each volume has a minimum and maximum number of cache slotsfor write operations

When a Symmetrix is IMPLed (Initial Microcode Program Load), the amount of available cache resources is

automatically distributed to all of the logical volumes in the configuration. For example, if a Symmetrix were

configured with 100 logical volumes of the same size and emulation, then at IMPL, each one would receive 1% of

available cache resources. As soon as reads and writes to volumes begins, the Symmetrix Operating Environment

(Enginuity) dynamically adjusts the allocation of cache. If only 1 of the 100 volumes was active, it would get

incrementally more cache and the remaining amount would be redistributed to the other 99 volumes. Managing each

individual volumes write activity enables Enginuity to typically prevent system-wide delayed write situations.





Enginuity Overview

z Operating Environment for Symmetrix Each processor in each director is loaded with Enginuity

Downloaded from service processor to directors over internal LAN

Zipped code loaded from EEPROM to SDRAM (control store of director)

Enginuity is what allows the independent director processorsto act as one Integrated Cached Disk Array Also provides the framework for advanced functionality like SRDF,

TimeFinder,...etc.

All DMX ship with the latest Enginuity

5670.73.69

Symmetrix Hardware

Supported:50 = Symm3

52 = Symm4

55 = Symm5

56 = DMX

MicrocodeFamily

(Major Release

Level)

Field Release Level ofSymmetrix Microcode

(Minor Release Level)

Field Release Level of

Service ProcessorCode

(Minor Release Level)

Non-disruptive microcode upgrade and load capabilities are currently available for the Symmetrix. Symmetrix takes

advantage of a multi-processing and redundant architecture to allow for hot loadability of similar microcode platforms.

The new microcode loads into the EEPROM areas within the channel and disk directors, and remains idle until

requested for hot load in control storage. The Symmetrix system does not require manual intervention on the

customers part to perform this function. All channel and disk directors remain in an on-line state to the host processor,

thus maintaining application access. Symmetrix will load executable code at selected windows of opportunity within

each director hardware resource, until all directors have been loaded. Once the executable code is loaded, internal

processing is synchronized and the new code becomes operational.





5670+ Management Features Enhancements

z 5670+ Management Features End User Configuration

User control of volumes and type Symm Purge

Secure deletion method

Logical Volumes Increased number of hypers

Volume Expansion Striped meta expansion

User Configuration - Enginuity v 5670+ will allow users to un-map CKD volumes, delete CKD volumes, or convert

CKD volumes to FBA. These user configuration controls will simplify the task of reusing a Symmetrix by not

requiring an EMC resource to modify the bin file.

Symm Purge - provides customers a secure method of deleting (electronic shredding) sensitive data. This willsimplify the reuse of drive assets.

Logical Volumes - v 5670+ will support an increased number of hypers per spindle. The number of hypers will

depend on the protection scheme.

Volume Expansion - Previous microcode versions only supported the expansion of concatenated meta volumes.

V5670+ will now support the expansion of both striped and concatenated meta volumes.





5670+ Business Continuity Features

z 5670+ Business Continuity Features SRDF/A

multi-session support Protected Restore

Enhanced restore features

SNAP Persistence Preserves snap session

SRDF/A- currently (v 5670) SRDF-A can only support a single-session. With v5670+ code, support will be available

for multi-session SRDF/A data replication. Multi-session uses host control (Mainframe only). Cycle switching is

synchronized between the single-session SRDF/A Symmetrix pairs.

Protected Restore- v 5670+ provides Protected Restore features. While the restore is in progress, read miss data will

come from the BCV, writes to the Standard volume will not propagate to the BCV, and the original Standard to BCV

relationship will be maintained.

SNAP Persistence - v 5670+allows a protected snap restore and preserves the virtual snap session when the restore

terminates.





Configuration Considerations

z Understand the applications on the host connected to the Symmetrix system Capacity requirements

I/O rates

Read/Write ratios Read/Write - Sequential or Random

z Understand special host considerations Maximum drive and file system sizes supported

Consider Logical Volume Manager (LVM) on the host and the use of data striping

Device sharing requirements - Clustering

z Determine Volume size and appropriate level of protection Symmetrix provides flexibility for different sizes and protection within a system

Standard sizes make it easier to manage

z Determine connectivity requirements

Number of channels available from each hostz Distribute workloads from the busiest to the least busy

The best possible performance will only be achieved if all the resources within the system are being equally utilized.

This is much easier said than done, but through careful planning, you will have a better chance for success. Planning

starts with understanding the host and application requirements. Within the Symmetrix bin-file, the emulation type,

size in cylinders, count, number of mirrors, and special flags (like BCV, DRV, Dynamic Spare) are defined. Each

Symmetrix Logical Volume is assigned a hexadecimal identifier. The bin file also tells the Channel director which

volumes are presented on which port, and the address used to access it. From the Hosts perspective, when a device

discovery process occurs, the information provided back to the OS appears to be referencing a series of SCSI disk

drives. To an Open Systems host, the Symmetrix looks like a JBOD (Just a Bunch Of Disks). The host is unaware of

the bin file, RAID protection, remote mirroring, BCV mirrors, dynamic sparing, ...etc. In other words, the host thinks

its getting an entire physical drive.





Symmetrix Configuration Information

z Symmetrix configuration informationincludes the following: Physical hardware that is installed

number and type of directors, memory,

and physical drives Mapping of physical disks to logical

volumes

Mapping of addresses tovolumes and to front-end directors

Operational parameters for front-enddirectors

z Configuration information is referred to asthe IMPL.bin file or simply the bin file

z Stored in two places: On the Hard Disk of the Symmetrix

Service Processor

In the EEPROM of each SymmetrixDirector

z Configuration changes can also be madeusing EMC ControlCenter ConfigurationManager GUI and Solutions Enabler CLI

Bin file stored in two places

Directors Service Processor

Two very important concepts:

Each director (both Channel and Disk) has a local copy (stored in EPROM) of the configuration file. This enables

Channel Directors to be aware of the Disk Directors that are managing the physical copy(ies) of Symmetrix LogicalVolumes and vice versa. The bin file also allows Channel Directors to map host requests to a channel address, or

target and LUN to the Symmetrix Logical Volume.

Changes made to the bin file (non-SDR changes) must first be made to the IMPL.BIN on the Service Processor and

then downloaded to the directors over the internal Ethernet LAN. Though Customer Service has the capability to do

remote bin file updates (using the EMC Remote application), standard operating procedure mandates the CE be

physically present for all configuration changes. In addition, CS requires that all CEs do a comparison analysis prior

to committing changes (the existing IMPL.BIN is compared to the proposed IMPL.BIN).





Disk Performance Basics

z Three components of disk performance

Time to reposition actuator - Seek time

Rotational latency Transfer rate

z With a Symmetrix, I/Os are servicedfrom cache not from the physical HDA

Minimizes the inherent latencies ofphysical disk I/O

Disk I/O at memory speeds

+ Transfer Rate

Transfer Data

Position

Actuator

Seek

timeDisk I/O =

time

+ Rotational Delay

Rotational Delay

When you look at a physical disk drive, a read or write operation has three components that add up to the overall

response time.

Actuator positioning is the time it takes to move the read/write heads over the desired cylinder. This is mechanicalmovement and is typically measured in milliseconds. The actual time that it takes to reposition depends on how far the

heads have to move, but this contributes to the greatest share of the overall response time.

Rotational Delay is the time it takes for the desired information to come under the ready write head. This time is the

function of the revolutions per second, or drive RPM. The faster the drive turns, the lower the rotational latency. A

10,000 RPM drive has an average rotational latency of approximately 3.00 milliseconds, which is half the time it takes

to make one revolution.

Transfer Rate is the smallest time component and consists of the time it takes to actually read/write the data. This is a

function of drive RPM and the data density. It is often measured as internal transfer rate or external transfer rate. The

external rate is the speed that the drive transfers data to the controller. This is limited by the internal transfer rate, but

with buffers on the drive modules themselves, it allows faster transfer rates.

The design objective of a Symmetrix is to not limit the performance of host applications based on the performance

limitations of the physical disk. This is accomplished using cache. Write operations are to cache and asynchronously

destage to disk. Read operations are from cache using the Least Recently Used algorithm and prefetching to keep the

information that is most likely to be accessed in memory.





Symmetrix Disk Comparisons

73 GB 146 GB181 GB73 GB36 GB18 GB36 GB 146 GB

Fibre

Channel

Fibre

Channel

Fibre

Channel

Ultra SCSIUltra SCSIUltra SCSIUltra SCSIUltra SCSIUltra SCSIInterface

DMXDMXDMXSym 5.XSym 5.XSym 5.XSym 5.XSym 5.XSym 4.8SymmetrixArchitecture

10,00015,00010,00010,00010,00010,00010,00010,0007,200

SpindleSpeed

73 GB

Symmetrix physical drives are manufactured by our supplier (Seagate, Hitachi) to meet EMCs rigorous quality

standards and unique product specifications. These specification include, dedicated microprocessors (that can be XOR

capable), the most functionally robust microcode available, and large onboard buffer memory (4MB 32MB).

Again, while the physical speed of disk drives does contribute to the overall performance, the Symmetrix design is formost read or write operations to be handled from cache.





Mapping Physical Volumes to Logical Volumes

z Symmetrix Physical Drives are split into Hyper Volume Extensions

z Hyper Volume Extensions (disk slices) are then defined as SymmetrixLogical Volumes

Symmetrix Logical Volumes are internally labeled with hexadecimal identifier(0000-FFFF)

Maximum number of Logical Volumes per Symmetrix configuration = 8192

PhysicalDrive

Logical

Volume

4.2 GB

LogicalVolume

4.2 GB

LogicalVolume

4.2 GB

LogicalVolume

4.2 GB

18 GB

While hyper -volume and split refer to the same thing (a portion of a Symmetrix physical drive), a logical

volume is a slightly different concept. A logical volume is the disk entity presented to a host via a Symmetrix

channel director port. As far as the host is concerned, the Symmetrix Logical Volume is a physical drive.

Do not confuse Symmetrix Logical Volumes with host-based logical volumes. Symmetrix Logical Volumes aredefined by the Symmetrix Configuration (BIN File). From the Symmetrix perspective, physical disk drives are being

partitioned into Hyper Volumes. A Hyper Volume could be used as an unprotected Symmetrix Logical Volume, a

mirror of a Symmetrix Logical Volume, a Business Continuance Volume (BCV), a parity volume for Parity RAID, a

remote mirror using SRDF, a Disk Reallocation Volume (DRV), etc. Host-based logical volumes are configured by

customers through Logical Volume Manager software (Veritas LVM, NT Disk Administrator, ...etc.).

Note: In actuality, the true useable capacity of the drive would be less than 18GB due to disk formatting and overhead

(track tables, etc.). This would result in each of the 4 splits in this example being approximately 4.21GB in size (open

systems).





Symmetrix Logical Volume Specifications

z Volume Specifications vary with Enginuity level

Enginuity allows up to 128 Hyper Volumes to be configured froma single Physical Drive

Size of Volumes defined as number of Cylinders (FBA Cylinder =15 * 32K), with a max. size ~32 GB

All Hyper Volumes on a physical disk do not have to be the same

size however a consistent size makes planning and ongoingmanagement easier

Physical

Disk

Physical

Disk

Physical

Disk

Physical

Disk

Physical

Disk

Volume specifications are illustrated here.





Defining Symmetrix Logical Volumes

z Symmetrix Logical Volumes are configured using the serviceprocessor and SymmWin interface/application

EMC Configuration Group uses information gatheredduring pre-site survey to create initial configuration

Generate configuration file (IMPL.BIN) that is downloaded from the serviceprocessor to each director

z Most configuration changes can be performed on-line at thediscretion of the EMC Customer Engineer

z Configuration changes can be performed online using theEMC ControlCenter Configuration Manager and SolutionsEnabler Command Line Interface

Physical

Disk

Physical

Disk

Physical

Disk

Physical

Disk

Physical

Disk

Symmetrix Service Processor

Running SymmWin Application

The C4 group (Configuration and Change Control Committee) is the division of Global Services responsible for initial

Symmetrix configuration and any subsequent changes to the configuration. They use time-honored and extensive best

practices and tools to configure Symmetrix. There is also much manual review to be done to ensure that BIN files are

valid. An important misperception to correct is that only the CE can change the bin-file. While this might have been

true at one time, today the customer may make configuration changes using EMC ControlCenter GUI or the Solutions

Enabler CLI.

Prior to 5x66 Enginuity, BIN file configuration was performed using a DOS-based program called AnatMain.





Symmetrix Logical Volume Types

z Open Systems hosts use Fixed Block Architecture (FBA) Each block is a fixed size of 512 bytes

Sector = 8 Blocks (4,096 Bytes)

Track = 8 Sectors (32,768 Bytes)

Cylinder = 15 Tracks (491,520 Bytes)

Volume size referred to by the number of Cylinders

z Mainframes use Count Key Data (CKD) Variable block size specified in count

Emulate Standard IBM volumes 3380D, E, K, K+, K++ (max. track size 47,476 bytes)

3390-1, -2, -3, -9 (max. track size ~ 56,664 bytes)

Volume size defined as a number of Cylinders

z Symmetrix stores data in cache in FBA and CKD and on physicaldisk in FBA format (32 KB tracks) Emulates expected disk geometry to host OS through Channel

Directors

Data Block

512 Bytes

DataCount Key

A notable exception to the 512-byte Open Systems rule is AS/400. It uses 520 bytes per block. The extra 8 bytes

are for host system overhead. Enginuity, prior to 5566 on the Symmetrix 5, only supports a single type of FBA format

on Open Systems drives. If you connect an AS/400 to a pre-5566 Symmetrix, all FBA devices must be formatted 520.

Open Systems hosts other than the AS/400 must be configured to use 520-formatted volumes. BE AWARE THAT

CHANGING THE LOW-LEVEL FORMAT OF PHYSICAL DEVICES TYPICALLY REQUIRES SYMMETRIX

DOWNTIME. Also, reformatting existing 512 devices will erase them, requiring a potentially complex backup and

restore of all Open Systems data. With 5566+ on Symm 5 +, Enginuity has SLLF (Selective Low-Level Format)

capabilities. This allows some drives to be formatted 512 and others 520, avoiding the complications mentioned

above.

The primary use for cache is for staging and destaging data between the host and the disk drives. Cache is allocated in

tracks and is referred to as cache slots, which are 32Kbytes in size (57 Kbytes for Mainframe). If the Symmetrix is

supporting both FBA and CKD emulation within the same frame, the cache slots will be the size of the largest track

size, 57K (3390) track size.





Logical

Volume 001

LogicalVolume 002

LogicalVolume 003

LogicalVolume 00F

Meta

Volume

LV 001

LV 002

LV 003

LV 00F

*Note: Symmetrix Engineering

recommends Meta Volumes no larger

than 512GB

Meta Volumes

z Between 2 and 255* SymmetrixLogical Volumes can be groupedinto a Meta Volume configuration

and presented to Open Systemhosts as a single disk

z Allows volumes larger than thecurrent maximum hyper volumesize of 32GB Satisfies requirements for

environments where there is alimited number of host addressesor volume labels available

z Data is striped or concatenatedwithin the Meta Volume

z Stripe size is configurable 2 Cylinders is the default size,

which is appropriate for mostenvironments

Meta Volumes allow customers to present larger Symmetrix Logical Volumes to the host environment. They are able

to present more GBs with fewer channel addresses. There is a limitation on the number of volumes a host can manage.

For example, with NT, the Drive lettering puts a limit on the number of volumes, and Meta Volumes prevent running

out of drive letters by presenting larger volumes to NT hosts.





Data Protection

z Data protection options are configured at the volume level and the samesystem can employ a variety of protection schemes

Mirroring (RAID 1)

Highest performance, availability and functionality

Two mirrors of one Symmetrix Logical Volume located on separate physical drives

Parity RAID

3 +1 (3 data and 1 parity volume) or 7 +1 (7 data and 1 parity volume)

Formerly known as RAID S or RAID R

RAID 5 Striped RAID Volumes

Data blocks are striped horizontally across the members of the RAID (4 or 8 volume) group

No separate parity drive, parity blocks rotate among the group members

RAID 10 Mirrored Striped Mainframe Volumes

Dynamic Sparing

One or more HDAs that are used when Symmetrix detects a potentially failing (or failed) device

Can be utilized to augment data protection scheme

Minimizes exposure after a drive failure and before drive replacement SRDF (Symmetrix Remote Data Facility)

Mirror of Symmetrix Logical Volume maintained in separate Symmetrix frame

RAID - Redundant Array of Independent Disks

The RAID Advisory Board has rated configurations with both SRDF and either Parity RAID or RAID 1 Mirroringwith the highest availability and protection classification: Disaster Tolerant Disk System Plus (DTDS+)

See http://www.raid-advisory.com/emc.html for the ratings.





Mirroring: RAID-1

z Two physical copies or mirrors of the data

z Host is unaware of data protection being applied

Physical

Drive

LV 001 M2

Different Disk

Director

Physical

Drive

LV 001 M1

Disk Director

Logical Volume001

Host Address

Target = 1LUN = 0

Mirroring provides the highest level of performance and availability for all applications. Mirroring maintains a

duplicate copy of a logical volume on two physical drives. The Symmetrix maintains these copies internally by

writing all modified data to both physical locations. The mirroring function is transparent to attached hosts, as the hosts

view the mirrored pair of hypers as a single logical volume.

Prior to the Symmetrix DMX, mirrors were configured with what is known as the rule of 17. Because of where

within the card cage the DA pairs reside (1/2, 3/4, 13/14, 15/16), as long as the sum of the DA director numbers equals

17 (1/16, 2/15, 3/14, 4/13), the mirrors will always be on different internal system buses for the highest availability and

maximum Symmetrix resources. The Symmetrix DMX uses the rule of 17 for director failover pairing, and not volume

mirroring. The point-to-point connections with cache eliminate the need for protection against a bus failure while

mirroring volumes.





Mirror Positions

z Internally each Symmetrix Logical Volume is represented by fourmirror positions M1, M2, M3, M4

z

Mirror position are actually data structures that point to a physicallocation of a mirror of the data and status of each track

z Each mirror positions represents a mirror copy of the volume or isunused

Symmetrix LogicalVolume 001

M1 M2 M3 M4M1 M3 M4

Before getting too far into volume configuration, understanding the concept of mirror positions is very important.

Within the Symmetrix, each logical volume is represented by four mirror positions M1, M2, M3, M4. These Mirror

Positions are actually data structures that point to a physical location of a data mirror and the status of each track. In

the case of SRDF, the mirror position actually points to a Logical Volume in the remote Symmetrix. Each position

either represents a mirror or is unused. For example, an unprotected volume will only use the M1 position to point to

the only data copy. A RAID-1 protected volume will use the M1 and M2 positions. If this volume was also protected

with SRDF, three mirror positions would be used, and if we add a BCV to this SRDF protected RAID-1 volume, all

four mirror positions would be used.





Physical

DrivePhysical

Drive

Logical Volume000

Logical Volume004

LogicalVolume 008

LogicalVolume 00C

LV 000 M1

LV 004 M1

LV 008 M1

LV 00C M1 LV 00C M2

LV 008 M2

LV 004M2

LV 000 M2

Mirrored Service Policy

z Symmetrix leverages either or both mirrors of a Logical Volume to fulfillread requests as quickly and efficiently as possible

z Two options for mirror reads: Interleave and Split Interleave maximizes throughput by using both Hyper Volumes for reads

alternately

Split minimizes head movement by targeting reads for specific volumes toeither M1 or M2 mirror

z Dynamic Mirror Service Policy (DMSP): policy is dynamically adjustedbased on I/O patterns Adjusted approximately every 5 minutes

Set at a logical volume level

During a read operation, if data is not available in cache memory, the Symmetrix reads the data from the volume

chosen for best overall system performance. Performance algorithms within Enginuity track path-busy information, as

well as the actuator location, and which sector is currently under the disk head in each device. Symmetrix performance

algorithms for a read operation choose the best volume in the mirrored pair based on these service policies.

Interleave Service Policy Share the read operations of a mirror pair by reading tracks from both logical

volumes in an alternating method: a number of tracks from the primary volume (M1) and a number of tracks

from the secondary volume (M2). The Interleave Service Policy is designed to achieve maximum throughput.

Split Service Policy Different from the Interleave Service Policy because read operations are assigned to

either the M1 or the M2 logical volumes, but not both. Split Service policy is designed to minimize head

movement.

Dynamic Mirror Service Policy (DMSP) -DMSP dynamically chooses between the Interleave and Splitpolicies at the logical volume level based on current performance and environmental variables, for maximum

throughput and minimum head movement. DMSP adjusts each logical volume dynamically based on recent

access patterns. This is the default mode. The Symmetrix system tracks I/O performance of logical volumes

(including BCVs), physical disks, and disk directors. Based on these measurements, it directs read operation for

mirrored data to the appropriate mirror. As the access patterns and workloads change, the DMSP algorithm

analyzes the new workload and adjusts the service policy to optimize performance.





Symmetrix RAID 10 (Mirrored Striped MainframeVolumes with DMSP)

To improve mainframe volume performance, Symmetrix RAID 10 stripes data of logical devices across multiple

Symmetrix logical devices.

Four Symmetrix devices (each one-fourth the size of the original mainframe device) appear as one mainframe device

to the host.Any four Symmetrix logical devices can be chosen to define a RAID 10 group provided they are the same type (for

example, IBM 3390) and have the same mirror configuration. Striping occurs across this group of four devices with a

striping unit of one cylinder, as shown in the diagram. Since each member of the stripe group is mirrored, the entire set

is protected. Dynamic Mirror Service Policy (DMSP) can then be applied to the mirrored devices. The combination

of DMSP with mirrored striping and concatenation to create a mainframe volume as illustrated, enables greatly

improved performance in mainframe system





Symmetrix RAID-10 Meta volume

M1 M2Host I/O

Vol A Vol A

Vol A Vol A

Vol A Vol A

Vol A Vol A

Cylinders

1, 5, 9..

Cylinders

2, 6, 10..

Cylinders

3, 7, 11..Cylinders

4, 8, 12..

Cylinders

1, 5, 9..

Cylinders

2, 6, 10..

Cylinders

3, 7, 11..Cylinders

4, 8, 12..

DMSP

This is a diagram of a RAID-10 stripe group. The portion of the logical volume which resides on one physical volume

is called a stripe. Each RAID-10 stripe group consist of four stripes distributed across four physical volumes. These are

mirrored to consist of eight total physical volumes. The stripe group is constructed by alternately placing one cylinder

across each of the four physical volumes. These physical volumes cannot be on the same DA. The eight physical

volumes are distributed across the Symmetrix back end for additional availability and improved performance. The

DMSP feature, which is available in all Symmetrix systems, allows the Enginuity algorithms to dynamically optimize

how the read requests can be satisfied over any of the eight physical devices.





Symmetrix Parity RAID

3 +1 (3 data volumes and 1 parity volume) or 7 +1.Parity calculated by Symmetrix Disk Drives using Exclusive-OR

(XOR) function.

Parity and difference data (result of XOR calculations) passedbetween drives by DAs.

Member drives must be on different DA ports (ideally ondifferent DAs).

Parity volumes distributed across member drives in RAIDGroup.

Vol A Vol B Vol C Parity

ABC

3 Host addressable volumes

+

Not host addressable

Parity RAID is also referred to as RAID-S in Symmetrix 5 and earlier architectures. EMCs Parity RAID DOES NOT

STRIPE DATA. Parity RAID employs the same technique for generating parity information as many other

commercially available RAID solutions, that is, the Boolean operation EXCLUSIVE OR (XOR). However, EMCs

Parity RAID implementation reduces the overhead associated with parity computation by moving the operation from

controller microcode to the hardware on the XOR-capable disk drives.

Symmetrix Parity RAID is not offered as a performance solution

For high data availability environments where cost and performance must be balanced

Fixed 3 + 1 configuration means 25% of disk space used for protection

Avoid in application environments that are 25% or greater write intensive

Every write to a data volume requires an update (write) to the parity volume within that rank or group

Write activity to the parity volume equals the total writes to the 3 data volumes within that rank or group

In write intensive environments, the parity volume is likely to reach its Fast Write Ceiling sending the entire

rank into delayed write mode

If customer requirements dictate using Parity RAID, planning and careful attention to layout is required to ensure

optimal performance. In some configurations, Parity RAID in a DMX environment may perform as well as RAID 1

protection on a Symmetrix 8000





Symmetrix RAID-5 (4 members)

Volume A

1 Host Addressable volume

Volume A with parity rotated among members

Parity 123 Data 1 Data 2 Data 3

Parity 456

Parity 789

Data 4 Data 5 Data 6

Data 7 Data 8 Data 9

Raid-5 Groups can have 4 or 8 members per logical device

4 members per logical device = 3 RAID-5

8 members per logical device = 7 RAID-5

This example shows a single Logical volume in a Raid-5 Group (Stripe width is 4 tracks).

Note that the data and parity tracks of a RAID-5 device are striped across 4 members.

No separate parity drive or volume; parity blocks rotate among the group members





Dynamic Sparing

z Dedicated spare(s) disk protects storage

z Disk errors are detected during I/Ooperations or through DAs Disk Scrubbing

z Data from failed disk is copied to DynamicSpare

z When failed disk is replaced, data isautomatically restored and Dynamic Spare

resumes role as standby

Dynamic

Spare

Every Symmetrix logical volume has 4 mirror positions. There is no priority associated with any of these positions.

They simply point to potential physical locations on the back end of the Symmetrix for the logical volume entity.

When sparing is necessitated, hyper volumes on the spare disk devices take the next available mirror position for the

logical volumes present on the failing volume. All of these dynamic spare hyper volumes are marked as having all

tracks invalid in the respective mirror positions of the logical volumes. It is now the responsibility of the Symmetrix to

copy all tracks over to the Dynamic Spare.

Dynamic sparing occurs at the physical drive level, since a physical drive is the FRU (Field Replaceable Unit) in the

Symmetrix. In other words, you cant just replace a failed hyper volume, only the disk it resides on. However, the

actual data migration from the volumes on the failed drive to the dynamic spare occurs at the logical volume level.

Dynamic Sparing is also supported with Parity RAID, a minimum of 3 spares is suggested. If a drive fails, a dynamic

spare drive will copy the data volumes onto itself by rebuilding them from parity and reading from any remaining

uncorrupted data. If there are at least 3 spares available, the 1st spare will also start copying data from uncorrupted

drives in the group. The other 2 spares will copy the contents of the remaining data volumes on the unaffected drives

in the group. This results in the formerly parity-protected volumes now being temporarily mirrored. Since parity cant

be calculated with a drive lost, and mirroring is a faster way to make sure the data is redundantly protected, mirroring

the entire RAID group results in the best way to protect against data loss until the problematic drive can be replaced.





SRDF Introduction

z Symmetrix Remote Data Facility (SRDF) maintains real-time or nearreal-time copy of data at remote location

z Similar concept as RAID-1 except mirror is located in a different

Symmetrixz Primary copy is called Source, remote copy is called Target

z Link options between local and remote Symmetrix based on distanceand performance requirements

ESCON

Fibre Channel

Gigabit Ethernet

Source Target

SRDF is an online, host-independent, mirrored data storage solution that duplicates production site data (source) to a

secondary site (target). If the production site becomes inoperable, SRDF enables rapid manual fail over to the

secondary site, allowing critical data to be available to the business operation in minutes. While it is easy to see this as

a disaster recovery solution, the remote copy can also be used for business continuance during planned outages as well

as backups, testing, and decision support applications. EMC offers a complete set of replication solutions to meet a

wide range of service level requirements. When implementing a remote replication solution, users must balance

application response time, recovery point objectives, and communications and infrastructure costs.





TimeFinder Introduction

z TimeFinder allows localreplication of SymmetrixLogical Volumes for business

continuance operations

z Utilizes special SymmetrixLogical volume called a BCVor Business ContinuanceVolume

BCV can be dynamicallyattached to another volume,synchronized, and split off

Host can access BCV as an

independent volume that maybe used for businesscontinuance operations

Full volume copy

1. Establish BCV

2. Synchronized

3. Split BCV

4. Execute BC operations

using BCV

STD BCV

BCV Split

BCV

Established

STD BCV

TimeFinder uses Business Continuance Volumes (BCVs) to create copies of a volume for parallel processing.

Basic TimeFinder operations include:

Establish Mirror relationship between any standard volume and BCV. Basically, the BCV assumes the next

available mirror position of the source volume. While a BCV is established, it is hidden from view andcannot be accessed.

Synchronize data from Source to BCV. Synchronization will take place while production continues on the

source volume. TimeFinder supports incremental establish by default where only changed data since the last

establish is synchronized.

Split allows the BCV to be accessed as an independent volume for parallel processing.

Restore allows the BCV to be established as a mirror to either the original source or a different volume and the

data on the BCV is synchronized.





EMC SNAP Introduction

zEMC SNAP uses Snapshot techniquesto create logical point-in-time images ofa source volume Snapshot is a virtual abstraction of a

volume

Multiple Snapshots can be created fromsame source

Snapshots are available immediately

zEMC SNAP does a Copy-on-Write Writes to production volume are first

copied to Save Area

Uses only a fraction of the sourcevolumes capacity (~2030%)

zSnapshots can be used for both readand write processing Reads of unchanged data will be from

Production volume

Changed data will be read from Save Area

Save Area

Production viewof volume

Snapshot viewof volume

Volume A

Original data copiedto Save Area prior to

new productionwrites

Snapshot

of

Volume A

(VDEV)

EMC Snap creates space-saving, logical point-in-time images or snapshots. The snapshots are not full copies of data;

they are logical images of the original information based on the time the snapshot was created. Its simply a view into

the data. A set of pointers to the source volume data tracks is created instantly upon activation of the snapshot. This

set of pointers is addressed as a logical volume and is made accessible to a secondary host that uses the point-in-time

image of the data.





Symmetrix Availability: Phone-Home and Dial-In

z EMC Phone-Home capability Service Processor connects to

external modem Communicates error and

diagnostic information to EMCCustomer Service

Provides problem resolutionz Dial-In capability

Product Support Engineer (PSE)or Customer Engineer (CE) dial-in

Allows full control of serviceprocessor through proprietary andsecure interface

Allows for proactive and reactivemaintenance

Can be disabled by customerthrough external modem

Every Symmetrix unit has an integrated service processor that continuously monitors the Symmetrix environment. The

service processor communicates with the EMC Customer Support Center through a customer-supplied, direct phone

line. The service processor automatically dials the Customer Support Center whenever Symmetrix detects a component

failure or environmental violation. An EMC Product Support Engineer at the Customer Support Center can also run

diagnostics remotely through the service processor to determine the source of a problem and potentially resolve it

before the problem becomes critical. When required, a Customer Engineers will be dispatched to the Symmetrix to

replace hardware or perform other maintenance.





Course Summary

The key points covered in this course include:

z Redundancy in the hardware design, and intelligence through

Enginuity, allow Symmetrix to provide the highest levels of dataavailability

z Symmetrix basic architecture is comprised of three functionalareas (Front End, Back End and Shared Global Memory)connected by internal system buses

z All I/O must be serviced through cache (read hit, read miss, fastwrite, delayed write)

z Symmetrix physical disk drives are divided into Hyper Volumes,which form Symmetrix Logical Volumes, that are presented to thehost environment as if they were entire physical drives

z Mirroring, Parity RAID, SRDF, and Dynamic Sparing are all mediaprotection options available on Symmetrix

These are some of the main features of the Symmetrix. Please take a moment to read them.


50/50



Closing Slide

Thank you for your attention. This ends our training on Symmetrix Foundations.

symmetrix foundations student resource guide[1]

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