© 2006 Hewlett-Packard Development Company, L.P. The information contained herein is subject to change without notice

EVA Concepts and terminology

Yu-Sheng Guo

Account Support Consultant

HP Taiwan

112/04/12 HP Restricted

Objectives

• Define the virtual storage terms applicable to the EVA

• Name the primary features of a disk group and default disk group

• Describe the ways in which disk groups are configured

• Name the primary features of virtual disks

• Differentiate between conventional RAID and distributed virtual RAID (VRAID) technology

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Virtual storage terminology

• Storage system (cell) — An initialized pair of HSV controllers with a minimum of eight physical disk drives

• Disk group — A group of physical disks, from which you can create virtual disks

• Virtual disk — A logical disk with certain characteristics, residing in a disk group

• Virtual disk leveling — Distribution of all user data within the virtual disks in a disk group across all physical disks within the disk group

• Distributed sparing — Allocated space per disk group to recover from physical disk failure in that disk group

• Host — A collection of host bus adapters that reside in the same (virtual) server

• Logical Unit Number (LUN) — A virtual disk presented to one or multiple hosts

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Storage system

• Also called a cell, an initialized pair of HSV controllers with a minimum of eight physical disk drives

• Requires a name up to 20 characters long– Special characters are not allowed (for example, ?, “, /, \)

– Two consecutive spaces are not allowed

– Name is changeable

• System initialization– Makes the storage system ready for use

– Binds the controllers together as an operational pair

– Creates the first disk group

– Establishes preliminary data structures on the disk array (metadata)

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Storage system metadata

• System-level metadata is stored on quorum disks and contains– Controller information

– WWN and cell name

– Character map of disk groups and virtual disk members

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Disk group

• A group of physical disks

• Maximum of 16 disk groups per array (7 for an eva3000)– Minimum number of physical disk drives in a disk group is 8– Maximum number of physical disk drives is the number

present in the system up to 240 (up to 56 for the eva3000)– Unassigned or new disks can be added to an existing group– Mixed drive sizes within a group are allowed

• Disk failure protection level– None, single, or double disk failures (not concurrent failure)– Default is none (sparing will occur from unassigned capacity)

• Space is allocated in 2MB segments (PSEGs)

• Chunk size is 256 blocks (128KB), fixed

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Default disk group

• First disk group created

• Used like any other disk group

• Can be deleted after another disk group is created to protect metadata

• Can be renamed

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Disk group metadata

• When a cell is created, there are five quorum disks in the default disk group

• Maximum of 16 quorum disks (one per disk group)

• When a new disk group is created– One quorum disk is created on it

– One quorum disk is removed from the default disk group until just one quorum disk remains

• Metadata overhead is 0.2% of total disk group capacity

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Disk group capacity

Disk group has two types of capacity•Assigned capacity

– Virtual disks, snapshots and clones– Spare space reserved for the

protection level

•Unassigned capacity – New virtual disk creation,

snapshots and clones– Freeing a physical disk for removal

or reassignment– Data reconstruction after disk

failure– Increases when virtual disks are

deleted or new physical disks are added to the disk group

Disk groupcapacity

Assigned

Unassigned

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Disk group member terms

• Unpaired — The disk that does not contain VRAID1 (mirrored) data on it because the disk group was created with an odd number of drives or because it lost its mirror partner because of a failure

• Paired — The disk that was previously unpaired. A disk was added to the group, which now contains an even number of disks.

Moderately redundant volume (VRAID5)

No redundancy volume (VRAID0)

Highly redundant volume (VRAID1)

VRAID1 pair VRAID1 pair VRAID1 pair VRAID1 pair

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Disk group creation

• Physical stores (Pstores)– Raw FC-AL disks

• Volumes– Pstores + metadata

• Logical disk allocation domain (LDAD)– Grouping of physical disks– Commonly called a disk group

Pstore Create volume Volume InsertLDAD

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Virtual disk

• A logical disk with certain attributes, such as size and VRAID level, residing in a disk group and spanning all members of the disk group

• Minimum size of 1GB and maximum size of 2TB (less 1GB)

• Maximum of 512 virtual disks

• VRAID levels for the virtual disks – VRAID0 or striping (none)

• Distributed across all disk in a group• 100% of disk group capacity

– VRAID5 or striping with parity (moderate)• Distributed across all disk in a group • Always five (4+1) physical disks per stripe are used• 80% of disk group capacity

– VRAID1 or mirroring (high)• Two physical disks per mirror are used• The odd drive in a disk group will not participate in this virtual disk• 50% of disk group capacity

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Virtual disk creation (1 of 2)

First written bit (first write overhead)• HSV tracks blocks written on a virtual disk

– Allows easy movement of data for snaps and clones– Zeros are not used in advance because operations

involving copies or moves would include the zeros

• First write to a block in a new LUN requires a metadata update

• Subsequent writes touch only the block, not metadata

• For normal uses with high I/O rates, overhead not an issue

• For performance testing, where write performance is critical, this overhead can be critical– Eliminate first-write overhead– Write all data blocks once before conducting a test

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Virtual disk creation (2 of 2)

Ldisks:Logical disks (containers)SCVDs: Storage cell virtual diskDunits: Derived unitsPunits:Presented units

LDADLDAD

metadata

LDisk

SCVD

DUnit

PUnit

Cache policy

Sizeredundancy

Writeprotect

LUN

Create unit

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Virtual disk map

• Contains pointers that identify which virtual disks use which chunks of capacity

• Map is read into HSV controllers during boot

• Map is written on state change of disk group – Disk drive failure

– Disk drives added or removed

– Traditional snapshot created

– Snapclone fully copied

– Virtual disk added or deleted

– Virtual disk enlarged

– Each write I/O to a virtual disk that has demand-allocated snapshot

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Virtual disk leveling (1 of 3)

• Distribution of all data within virtual disks proportionally across all physical disks within the disk group

• Leveling takes place when– Disk devices are added to a disk group

• Disk devices can be added one or more at a time

– Disk devices are ungrouped from a disk group

• You can only do this one disk at a time

– Disk devices within a disk group fail (assuming VRAID survival)

• Leveling is dynamic (there is no user control)

• Leveling is detectable through Command View EVA

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Virtual disk leveling (2 of 3)

Virtual disk blocks are automatically relocated to level spindle use

Moderately redundant volume (VRAID5)

No redundancy volume (VRAID0)

Highly redundant volume (VRAID1) +

Add more disks

Additional storage space available

No redundancy volume (VRAID0)

Highly redundant volume (VRAID1)

Moderately redundant volume (VRAID5) Available storage space (equivalent of 3 disks)

VRAID1 pair VRAID1 pair VRAID1 pair VRAID1 pairVRAID1 pairVRAID1 pair

VRAID1 pair VRAID1 pair VRAID1 pairVRAID1 pair

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Virtual disk leveling (3 of 3)

Leveling takes place when disk group members vary in size

• Example 1: Disk group = 10 drives, all 36GB – If a virtual disk is created using all of the drives, each

36GB disk contains an equal share (10%) of the capacity

• Example 2: Disk group = 10 drives, 5*36GB, 5*72GB– If a virtual disk is created using all of the drives

• Each 36GB and 72GB disk contains a proportional share of the capacity

• The proportion maintained in this example must be 1:2

• Proportional amounts of disk capacity are used whatever virtual disk capacity is created

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Virtual disk expansion

• Once a virtual disk is created, you can increase the size, but not decrease it

• Supported on Sun Solaris with the growfs command

• Supported on Windows 2000

• It is not supported on any other operating system– Workarounds are available

– Described in installation and configuration guides for each OS

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Hosts and LUNs

• A host is a collection of host bus adapters that reside in the same (virtual) server

• A LUN is a virtual disk presented to one or multiple hosts

• Rules for hosts, connections, and LUNs– A maximum of 256 hosts

– A maximum of 1,024 Fibre Channel adapter connections

– A maximum of 256 LUNs on any one Fibre Channel adapter

– A maximum of 8,192 presentations of LUNs to hosts

• Examples:

1 LUN presented to 1 host = 1 presentation

1 LUN presented to 256 hosts = 256 presentations

256 LUNs presented to 1 host each = 256 presentations