snapview snapshot

Copyright © 2014 EMC Corporation. All Rights Reserved.

SnapView Snapshot

Upon completion of this module, you should be able to:• Describe SnapView Snapshot operations• Configure and Manage SnapView Snapshots

SnapView Snapshot 1


SnapView Snapshots

During this lesson the following topics are covered: • Purpose of SnapView Snapshot• SnapView Snapshots requirements• SnapView Snapshots managed objects• SnapView Snapshots theory of operations

Lesson 1: Theory and Operation

SnapView Snapshot 2


SnapView Snapshots • SnapView Snapshot - an instantaneous frozen virtual copy of a

LUN on a storage system Allows a secondary server to view a point-in-time copy of a source

LUN Snapshots are created instantly – no data is copied at creation time Snapshot will not change UNLESS the user writes to it Original view available by deactivating changed Snapshot

• Virtual LUN Not a real LUN - made up of pointers, original and saved blocks Uses a copy on first write (COFW) mechanism Requires a ‘save area’ – the Reserved LUN Pool

SnapView Snapshot 3


SnapView Snapshots Requirements Environment System Requirements

Hardware VNX Storage SystemTwo or more Servers (if the SnapView snapshot is to be accessed by a host), each attached to the VNX that will run SnapView

Storage System Software VNX Operating Environment for BlockSnapView enabler

Management Software Unisphere UINavisphere Secure CLIAdmsnap

Operating Systems HP-UXIBM AIXLinuxSolarisWindows Server

Refer to EMC Support Matrix for a complete list

SnapView Snapshot 4


SnapView Snapshots Managed Objects• Source LUN

The LUN containing production data• SnapView Session

Process of defining the point-in-time designation Invokes COFW activity for updates to the source LUN

• Reserved LUN Supports the pointer-based design of SnapView Snapshot Used to save data chunks

• SnapView Snapshot The defined virtual LUN Presented to the secondary host Enables visibility into running sessions

SnapView Snapshot 5


SnapView Session • SnapView Session

COFW mechanism starts and ends with session SnapView snapshot appears off-line until there is an active session A multiple Source LUN session can be started consistently

• SnapView Session name Sessions should have significant names Compatibility with admsnap – use alphanumerics, underscores It’s case-sensitive!

• Session consistent start Holds I/O until session starts on all source LUNs Fails if any source LUN fails Does not allow other LUNs to be added to session

SnapView Snapshot 6


Copy on First Write• Allows efficient utilization of copy space

Uses a dedicated save area – the Reserved LUN Pool Total capacity of Reserved LUN Pool LUNs is approximately 20% of

total source LUN sizes• Saves original data chunks – once only

Chunks are a fixed size - 64 KB (128 blocks) Chunks are saved when they’re modified for the first time

• Allows consistent ‘point-in-time’ views of LUN(s)• Allows rollback to previous points in time

SnapView Snapshot 7


Reserved LUN Recommendations• Total number of Reserved LUNs is VNX model-dependent• Reserved LUNs may be of different sizes• No checking of size, disk type or RAID type when allocated• Use SAS drives with write-cache enabled LUNs• Thin LUNS cannot be used in the RLP• Create 2 RLs per Source LUN, each 10% of Source LUN size• Example

LUNs to be snapped: 10 GB, 20 GB, 30 GB, 100 GB Average LUN size = 160 GB/4 = 40 GB Make each Reserved LUN 4 GB in size Make 8 Reserved LUNs

SnapView Snapshot 8


SnapView: Stopping Sessions• Sessions may be manually stopped by the user • SnapView Sessions are automatically stopped

If the Reserved LUN Pool fills (attempt to use too much disk space)• Stopping the SnapView Session

Removes all memory map entries associated with session Reserved LUN Pool space is made available for reuse

SnapView Snapshot 9


Host I/O to a Source LUN• Three possible types of I/O to a source LUN

1. Read or write request with no active session I/O passed to driver below in I/O stack

2. Read request with active session I/O passed to driver below in I/O stack

3. Write request with an active session If the original data is not already in the Reserved LUN Pool, Copy on

First Write is performed Original data read from source LUN SnapView finds an unused area in the Reserved LUN Pool Original data written to unused area in Reserved LUN Pool Entry made in memory and on disk to indicate where original data is

written Write request passed to driver below in I/O stack

If the original data is already in the Reserved LUN Pool, the write request is passed to driver below in I/O stack

SnapView Snapshot 10


Host I/O to a Snapshot• Three possible types of I/O to a Snapshot

1. Read or write request with no active session is intercepted by the SnapView driver I/O requests fail – drive appears off-line

2. Read request with an active session Memory map consulted to determine if the data should be read from

the Reserved LUN Pool or from the source LUN3. Write request with an active session

Write requests are allowed; however, any data written to a Snapshot is not persistent beyond the end of the session

The memory map is consulted to determine if the original data has been written to the Reserved LUN Pool (i.e., COFW has already occurred)

If not, a new map entry is created, and the original data is written to the RLP. The new data is written to the Source LUN



SnapView Snapshot Theory of Operation


8AM 9AM

ProductionServer

A B C

SourceLUN

Chunks

A B CChunks

Session 9AM

LUN 6 LUN 7

LUN 8 LUN 9

Reserved LUN Pool

SourceLUN

ContinuousI/O

1 Session 9AM is started

Reserved LUN 6 is allocated

COFW is enabled

1

1


SnapView Snapshot Theory of Operation (continued)


10AM

A B C

Source LUN

Chunks

Session 9AM

LUN 6 LUN 7

LUN 8 LUN 9

Reserved LUN Pool

A B CChunks

Snapshot ofSource LUN

2 Snapshot of Source LUN is createdbut not activated2

Server BSnapshot of Source LUN is addedto the Storage Group of Server B

3

3Not Ready

ProductionServer

R / W




A B C

Source LUN

Chunks

LUN 6 LUN 7

LUN 8 LUN 9

Reserved LUN Pool

4 Snapshot of Source LUN is activated

4


A B CChunks

Session 9AM

Session 9AM is allocated by Snapshotof Source LUN

Server B

ProductionServer

11AM

R / W

R / W

Virtual Source LUN (Snapshot of Source LUN)is made available (R / W) to Server BA B C

Chunks




A B C

Source LUN

Chunks

LUN 6 LUN 7

LUN 8 LUN 9

Reserved LUN Pool

5 Production Server requests a changeon Chunk “C” (COFW)

5


A B CChunks

Session 9AM

Server B

ProductionServer

12PM

R / W

R / W

C’

6C

6 Original Chunk “C” is copied to theReserved LUN 6 allocated by Session 9AM




A B C’

Source LUN

Chunks

LUN 6 LUN 7

LUN 8 LUN 9

Reserved LUN Pool

7 Session 9AM pointer uses the originalChunk ‘C” from Reserved LUN 6


A B CChunks

Session 9AM

Server B

ProductionServer

12PM

R / W

R / W

7

C




A B C’

Source LUN

Chunks

LUN 6 LUN 7

LUN 8 LUN 9

Reserved LUN Pool

8


A B CChunks

Session 9AM

Server B

ProductionServer

1PM

R / W

R / W

8

C

B’

Server B requests a change on Chunk “B” (COFW)

B

9

9

Original Chunk “B” is copied to theReserved LUN 6 allocated by Session 9AMand then modified by the write

B’

’




A B C’

Source LUN

Chunks

LUN 6LUN 7

LUN 8 LUN 9

Reserved LUN Pool


A B’ CChunks

Server B

ProductionServer

1PM

R / W

R / W CB’

Session 9AM

Session 9AM pointer usesChunk B’ from Reserved LUN 6

01

01

B


SnapView Snapshots

During this lesson the following topics were covered:• Purpose of SnapView Snapshot• SnapView Snapshots requirements• SnapView Snapshots managed objects• SnapView Snapshots theory of operations

Lesson 1: Summary



SnapView Snapshots

During this lesson the following topics are covered: • Managing the Reserved LUN Pool• Managing SnapView sessions and SnapView snapshots • Configuring and managing SnapView sessions and SnapView

snapshots with the Wizards

Lesson 2: Configuring and Managing SnapView Snapshots



Reserved LUN Pool Management

21SnapView Snapshot


Reserved LUN Pool LUNs – Free LUNs

22SnapView Snapshot


Reserved LUN Pool – Allocated LUNs

23SnapView Snapshot


Monitoring Reserved LUN Pool UsageStorage System > System > Monitoring and Alerts > SP Event Logs

24SnapView Snapshot


SnapView Sessions

25SnapView Snapshot


SnapView Session PropertiesStorage System > Data Protection > Snapshots > LUN Snapshots

26SnapView Snapshot


SnapView Session – Start / Stop

27SnapView Snapshot


SnapView Snapshot

28SnapView Snapshot


Snapshot Session Rollback

29SnapView Snapshot


Snapshot Session Rollback Properties

30SnapView Snapshot


Snapshot Configuration Wizard

31SnapView Snapshot


SnapView Snapshots

During this lesson the following topics were covered:• Managing SnapView snapshots and SnapView sessions• Configuring and managing SnapView snapshots and sessions

with the Snapshot Wizard

Lesson 2: Summary

32SnapView Snapshot


SummaryKey points covered in this module:• SnapView Snapshot is an instantaneous frozen virtual copy of a

LUN on a VNX storage system• SnapView Snapshot uses COFW technology• Snapshot Wizard can be used to Configuring and managing

SnapView snapshots and sessions


snapview snapshot

Documents

snapview snapshot copyright

snapview feature

snapview snapshot2 copyright

snapview snapshot1 copyright

real lun

emc corporation

reserved lun pool operations

chunks of data