ece 6160: advanced computer networks

ECE 6160: Advanced Computer Networks

SAN

Instructor: Dr. Xubin (Ben) He

Email: [email protected]

Tel: 931-372-3462

Course web: http://www.ece.tntech.edu/hexb/616f05

mailto:[email protected]

ECE6160:Advanced Computer Networks

2

Prev…

• Networked storage

• NAS


3

Storage Architectures


4

Storage Area Networks


5

SAN connection

• FC:– FC-SAN

• LAN (Ethernet)– IP-SAN

– iSCSI

• Other networks– Petal (ATM)


6

Typical SAN

•Backup solutions (tape sharing) •Disaster tolerance solutions (distance to remote location) •Reliable, maintainable, scalable infrastructure


7

A real SAN.


8

NAS and SAN shortcomings

• SAN Shortcomings--Data to desktop--Sharing between NT and UNIX--Lack of standards for file access and locking

• NAS Shortcomings--Shared tape resources--Number of drives--Distance to tapes/disks

• NAS--Focuses on applications, users, and the files and data that they share

• SAN--Focuses on disks, tapes, and a scalable, reliable infrastructure to connect them

• NAS Plus SAN--The complete solution, from desktop to data center to storage device


9

NAS plus SAN.

•NAS Plus SAN--The complete solution, from desktop to data center to storage device


10

Petal/Frangipani

PetalPetal

FrangipaniFrangipani

NFSNFS

““SAN”SAN”

““NAS”NAS”


11

Petal/Frangipani

PetalPetal

FrangipaniFrangipani

NFSNFSUntrustedOS-agnostic

FS semanticsSharing/coordinationDisk aggregation (“bricks”)Filesystem-agnosticRecovery and reconfigurationLoad balancingChained declusteringSnapshotsDoes not control sharing

Each “cloud” may resize or reconfigure independently.What indirection is required to make this happen, and where is it?


12

Remaining Slides

The following slides have been borrowed from the Petal and Frangipani presentations, which were available on the Web until Compaq SRC dissolved. This material is owned by Ed Lee, Chandu Thekkath, and the other authors of the work. The Frangipani material is still available through Chandu Thekkath’s site at www.thekkath.org.

For ECE6160, several issues are important:• Understand the role of each layer in the previous slides, and the strengths and limitations of each layer as a basis for innovating behind its interface (NAS/SAN).• Understand the concepts of virtual disks and a cluster file system embodied in Petal and Frangipani.•Understand how the features of Petal simplify the design of a scalable cluster file system (Frangipani) above it.

http://www.thekkath.org/

Petal: Distributed Virtual Disks

Systems Research Center

Digital Equipment Corporation

Edward K. Lee

Chandramohan A. Thekkath

04/13/23


14

Logical System View

/dev/vdisk1/dev/vdisk2 /dev/vdisk3 /dev/vdisk4

/dev/vdisk5

AdvFS NT FS PC FS UFS

Scalable Network

Petal


15

Physical System View

Scalable Network

Petal Server Petal Server Petal Server Petal Server

Parallel Database or Cluster File System

/dev/shared1


16

Virtual Disks

• Each disk provides 2^64 byte address space.

• Created and destroyed on demand.

• Allocates disk storage on demand.

• Snapshots via copy-on-write.

• Online incremental reconfiguration.


17

Virtual to Physical Translation

PMap0

vdiskID

offset

(disk, diskOffset)

PMap1

Virtual Disk Directory

GMap

PMap2 PMap3

(server, disk, diskOffset)(vdiskID, offset)

Server 0 Server 1 Server 2 Server 3


18

Global State Management

• Based on Leslie Lamport’s Paxos algorithm.

• Global state is replicated across all servers.

• Consistent in the face of server & network failures.

• A majority is needed to update global state.

• Any server can be added/removed in the presence of failed servers.


19

Fault-Tolerant Global Operations

• Create/Delete virtual disks.

• Snapshot virtual disks.

• Add/Remove servers.

• Reconfigure virtual disks.


20

Data Placement & Redundancy

• Supports non-redundant and chained-declustered virtual disks.

• Parity can be supported if desired.

• Chained-declustering tolerates any single component failure.

• Tolerates many common multiple failures.

• Throughput scales linearly with additional servers.

• Throughput degrades gracefully with failures.


21

Chained Declustering

D0

Server0

D3

D4

D7

D1

Server1

D0

D5

D4

D2

Server2

D1

D6

D5

D3

Server3

D2

D7

D6


22

Chained Declustering

D0

Server0

D3

D4

D7

Server1

D2

Server2

D1

D6

D5

D3

Server3

D2

D7

D6

D1

D0

D5

D4


23

The Prototype

• Digital ATM network.– 155 Mbit/s per link.

• 8 AlphaStation Model 600.– 333 MHz Alpha running Digital Unix.

• 72 RZ29 disks.– 4.3 GB, 3.5 inch, fast SCSI (10MB/s).

– 9 ms avg. seek, 6 MB/s sustained transfer rate.

• Unix kernel device driver.

• User-level Petal servers.


24

The Prototype

src-ss1

Digital ATM Network (AN2)

src-ss2 src-ss8

petal1 petal2 petal8

/dev/vdisk1

/dev/vdisk1 /dev/vdisk1 /dev/vdisk1

………

………


25

Throughput Scaling

0

2

4

6

8

0 2 4 6 8

Number of Servers

Th

rou

pu

t S

cale

-up LINEAR

512B Rd

8KB Rd

64KB Rd

512B Wr

8KB Wr

64KB Wr


26

Virtual Disk Reconfiguration

0

5

10

15

20

25

30

0 1 2 3 4 5 6

Elapsed Time in Minutes

Th

rou

gh

pu

t in

MB

/s

6 servers

8 servers

virtual disk w/ 1GB of allocated storage8KB reads & writes

Frangipani: A Scalable Distributed File System

C. A. Thekkath, T. Mann, and E. K. Lee

Systems Research Center

Digital Equipment Corporation


28

Why Not An Old File System on Petal?

• Traditional file systems (e.g., UFS, AdvFS) cannot share a block device

• The machine that runs the file system can become a bottleneck


29

Frangipani

• Behaves like a local file system– multiple machines cooperatively manage

a Petal disk

– users on any machine see a consistentview of data

• Exhibits good performance, scaling, and load balancing

• Easy to administer


30

Ease of Administration

• Frangipani machines are modular– can be added and deleted transparently

• Common free space pool – users don’t have to be moved

• Automatically recovers from crashes

• Consistent backup without halting the system


31

Components of Frangipani

• File system core– implements the Digital Unix vnode interface

– uses the Digital Unix Unified Buffer Cache

– exploits Petal’s large virtual space

• Locks with leases

• Write-ahead redo log


32

Locks

• Multiple reader/single writer

• Locks are moderately coarse-grained– protects entire file or directory

• Dirty data is written to disk before lock is given to another machine

• Each machine aggressively caches locks– uses lease timeouts for lock recovery


33

Logging

• Frangipani uses a write ahead redo log for metadata

– log records are kept on Petal

• Data is written to Petal– on sync, fsync, or every 30 seconds

– on lock revocation or when the log wraps

• Each machine has a separate log– reduces contention

– independent recovery


34

Recovery

• Recovery is initiated by the lock service

• Recovery can be carried out on any machine– log is distributed and available via Petal


35

References

• E. Lee and C. Thekkath, “Petal: Distributed Virtual Disks,” Proceedings of the international conference on Architectural support for programming languages and operating systems (ASPLOS 1996)

• P. Sarkar, S. Uttamchandani, and K. Voruganti, “Storage Over IP: When Does Hardware Support Help?” Proc. of 2nd USENIX Conference on File And Storage Technologies (FAST’2003)

• C. Thekkath, T. Mann, and E. Lee, “Frangipani: A scalable distributed file system,” Proceedings of the 16th ACM Symposium on Operating Systems Principles (SOSP), pp. 224-237, October 1997

ece 6160: advanced computer networks

Documents

petal disk users

features of petal

disk storage

virtual disk reconfiguration

networks petal atm

servers virtual disk

real san

concepts of virtual