ETERNUS DX Advanced Copy Functions - Fujitsu · • Is active and recording as long as the Snap...

ETERNUS DX Advanced Copy Functions

Snapshots

Copyright Fujitsu, Release May 2011

Content

General Introduction to Snapshots Introduction to SnapOPC Introduction to SnapOPC+ Introduction to Snap Data Pool

Copyright Fujitsu, Release May 2011 Snapshots ETERNUS DX Advanced Copy Functions 2

General Introduction to Snapshots

Snapshots in General Two Types of Snapshots Snapshot Mechanism Backup Data Control Information Snapshot Feature Overview


Snapshots in General (1) Snapshots require the use of several bitmaps Standard OPC control bitmap is not used Per Snapshot session a tracking bitmap is in use

• Records subsequent changes at the source and destination volume • Is active and recording as long as the Snap session is active • Will be created for each Snap session, even if they have the same source

volume Logical Copy Initiating a Snap session

• Causes a tracking bitmap to be created • This is the initial logical copy step

Physical Copy There is no initial physical copy that starts the sequential transfer of the

whole contents of the source area to the destination When a modification is done on the Source Volume, then:

• Old data is copied to the active SDVs related to this Source Volume • New data is written to the source volume • Bits of the relevant tracking bitmap are changed to "modified"


Snapshots in General (2) SnapOPC Launching a Snap


Source

Monday

Tuesday

Wednesday

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SnapOPC

SnapOPC manages the copy source and copy destination in units of sessions, so generation management is not available. Copy source changes are copied to all sessions.

Snapshots ETERNUS DX Advanced Copy Functions 5

Snapshots in General (3) SnapOPC Writing new data in the Source Volume


Source

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Monday

Tuesday

Wednesday

SnapOPC


Write new data


Snapshots in General (4) Difference between SnapOPC and SnapOPC+


Source Source

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SnapOPC+ manages the data generations in units of sessions. The updated data in the copy course is copied to the latest session only. The generations must be searched to find a particular piece of data.

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1st generation

2nd generation

3rd generation

SnapOPC


Write new data 1st generation

2nd generation

3rd generation

SnapOPC+


Snapshot Mechanism (1) Copy on first write When a block on the copy source is updated the first time, the original

data from updated area is physically copied to the destination volume There is no initial copy generation available

The Destination Volume Must be pre-created on the ETERNUS side Is a special type of data volume named Snap Data Volume "SDV" Can be mapped and accessed as a normal volume from server side Has a physical and virtual capacity

• Only the virtual capacity is visible to the server • The physical capacity provides the original (old) data after source modification is done • The virtual capacity provides both unmodified and modified data

The Snap Data Volume (SDV) stores After source write: the original source data that was overwritten After destination write: modified data that was written to the SDV directly


Snapshot Mechanism (2) SDVs has to be created with the ETERNUS Manager GUI, in

the same way as a standard data volume, including couple of additional parameter settings SDV capacity can be much smaller than the source capacity The SDV capacity includes the Backup Data Control information which

equals approximately 0.1% of the Source Volume virtual capacity The virtual capacity is sometimes also named "source volume capacity"

• This parameter is only used when configuring SDVs, it is a virtual size and has to be the same capacity as of the Source Volume


Source LUN

Phy

sica

l cap

acity

Virtu

al c

apac

ity

Destination LUN

SDV

Phy

sica

l ca

paci

ty

Backup Data Control information • Conversion table

• Mapping virtual blocks to physical blocks


Snapshot Mechanism (3) Creating a SDV with the ETERNUS Manager GUI


DX400 and DX8000 systems DX60, DX80 and DX90 systems

Please note the screenshots may look different depending on the firmware version. Snapshots ETERNUS DX Advanced Copy Functions 10

Backup Data Control Information (1) As already mentioned on the previous pages, BDC is included

in the physical capacity of the SDV Snapshot Tracker

• Resides in the Controller Module cache of the ETERNUS DX • Tracking data (update history) is kept as a copy status bitmap in the cache

memory • Multiple update history bitmaps are used to locate each piece of data one per

session/generation


Tracker used for • SnapOPC • SnapOPC+

Multiple SDVs to be managed as an update history


Backup Data Control Information (2) Conversion Table Is used to convert the virtual addresses (LBA: Logical Block Address; V)

to a real addresses (LBA: Logical Block Address; R)






Approx. 30% to 50% of source capacity


Backup Data Control Information (3) Snap Data Volume The actual destination copy volume size can be rather small in

comparison to the Source Volume, as only modified destination blocks and copied originals of modified source blocks are stored

To get an estimated value - based on an average modification - for the SDV capacity, ACM provides a test command "swstestupdate" • For more details refer to chapter Commands in the ACM Operator's Guide


Snapshot Feature Overview (1) The physical copy destination (SDV) Only needs to be large enough to contain the updated areas,

consequently size requirements are usually small

Performance is lower than for a normal volume since the logical copy destination volume is generated from two sources Original data of the copy source Modified data kept in the physical copy destination

When multiple Snap sessions are set for one copy source With SnapOPC the old data is physically copied to all copy destinations With SnapOPC+ only to the latest copy destination

Up to eight1) Snap sessions can be set on one copy source Cascade copy using a Snap Destination Volume as the copy

source is not supported In other words SDV can not be the source of the next copy session


1) At the time of publication, please refer to latest documentation for up-to-date status. Snapshots ETERNUS DX Advanced Copy Functions 14

Snapshot Feature Overview (2) Advantages Copy is created and accessible instantly (bitmap table used to track data) Physical copy destination only needs to be large enough to contain the

updated areas Suitable usage Work area backup to tape

• Source volume can resume operation immediately • Backup software saves the complete source data from the SDV even if there

are blocks modified Backup against operation and software errors Disadvantage Access performance to source volume is degraded Data cannot be fully restored if the source volume is not available Unsuitable usage Copy of volume with frequent updates Copy of volume which requires access performance Backup against hardware failures

• Source volume must be available


Introduction to SnapOPC

SnapOPC Single Block Updates SnapOPC Multiple Block Updates SnapOPC Restore SnapOPC Read and Write Operations Executing SnapOPC Restore


SnapOPC Single Block Updates Any source data block change is recorded only once per

session Only the first modification of a data block will be copied to the destination

volume "SDV"


SnapOPC (1)

Source

SnapOPC (2)

1

1

1

1

SDV1

SDV2

Step1 start

Step5

Step4 start

Step3

Step2

Step6

1

1 1

1

1

1

1

1

1 1

1 1

1

1

1

1

1


SnapOPC Multiple Block Updates How SnapOPC handles modifications on several blocks In step 1 with the first SnapOPC session working with SDV1 And in step 4 with another SnapOPC session working with SDV2


SnapOPC (1)

Source

SnapOPC (2)

1

1

1

SDV1

SDV2

Step1 start

Step5

Step4 start

Step3

Step2

Step6

1 1

2 1

1

1

3

2

3

2 2

3

2 3

2

2

3

3

2 3

2 3

2

1 2 3

3

2

3

2 3 2

1 1


SnapOPC Restore How SnapOPC restores data from several SDVs Depends on the SDV source selection and which data is to be restored to

the original Source Volume


SnapOPC (1)

SnapOPC (2)

Step1 start

Step5

Step4 start

Step3

Step2

Step6

Source

1 2 3

1 2 3

1 2 3

1 2 3

1 2 3

SDV1

1 2 3

SDV2

2 3

1 2 3

Source after restore from SDV1

1 2 3

Source after restore from SDV2

1 2 3 Source

Source data accessible

after step 6


SnapOPC Read and Write Operations (1) Reading data from the source disk Area to be read is fetched normally directly from the copy source Note: The copy destination "SDV" contains only the data that has been

modified


Copy Source Volume

Copy Destination Volume

Host View (virtual LUN seen to have the same capacity as the copy source)

Snap Data Volume (physically smaller capacity where the actual snap data is stored)

Application read SnapOPC Tracker

Within CM cache


SnapOPC Read and Write Operations (2) Reading data from the destination disk Area to be read is checked in the SnapOPC tracker

• Data that has not been changed is taken from the copy source


Copy Source Volume




Application reads unmodified data

SnapOPC Tracker Checks

data status


SnapOPC Read and Write Operations (3) Writing data to the source disk When a section of the source volume is overwritten

• Old data (here white colored) is copied from source to physical destination • The area is marked as "changed" in SnapOPC Tracker • New data (here striped) is written to copy source


Copy Source Volume




Application writes SnapOPC Tracker Modifies

data status


SnapOPC Read and Write Operations (4) Reading backed up data from the destination disk Area to be read is flagged by the SnapOPC tracker

• Data that has been changed is fetched from the physical copy destination "SDV"


Copy Source Volume




Application reads modified data

SnapOPC Tracker Checks

data status


SnapOPC Read and Write Operations (5) Writing data to an unmodified block at the destination disk Area to be written with new data is flagged by the SnapOPC tracker


Copy Source Volume




Application writes

SnapOPC Tracker Modifies

data status


SnapOPC Read and Write Operations (6) Writing data to a backed up block of the destination disk Area to be written with new data is flagged by the SnapOPC tracker

• Data that has been changed is written to the physical copy destination "SDV"


Copy Source Volume




Application writes

SnapOPC Tracker Modified

data status


Executing SnapOPC Restore (1) To restore from one of the target volumes (SDV) There is no full backup of the source data available with SnapOPC


Session 1

Session 3

Session 4

T1

T2

T3

T4

Session 2

S


Executing SnapOPC Restore (2) To restore from one of the target volumes (SDV) You must cancel ALL OTHER SnapOPC sessions operating on the same

source volume


Session 1

Session 2

Session 3

Session 4

Session 1

Restore

Session 3

Session 4

S

T1

T2

T3

T4

S

T1

T2

T3

T4

Session 2 Session 2


Introduction to SnapOPC+

SnapOPC+ Single Block Updates SnapOPC+ Multiple Block Updates SnapOPC+ Read and Write Operations Executing SnapOPC+ Restore


SnapOPC+ Single Block Updates Any source data block change is recorded only once per

session Only the first modification of a data block will be copied to the destination

volume "SDV"


Source

1

1

1

1

SDV1

SDV2

Step 1 start SnapOPC+ (1)

Step 5


Step 3

Step 2

Step 6

1

1 1

1

1

1

1

1 1

1

1 1

1

1

Snapshots ETERNUS DX Advanced Copy Functions

1

29

SnapOPC+ Multiple Block Updates How SnapOPC+ handles modifications on several blocks In step 1 with the first SnapOPC+ session working with SDV1 And in step 4 with another SnapOPC+ session working with SDV2


Source

1

1

1

1

SDV1

SDV2


Step 5


Step 3

Step 2

Step 6

1 1

2 1

1

1

1

3

2 2

3

2 3

2

2

3

3

2 3

2 3

2

1 2

3

2

3

2 2


SnapOPC+ Block Restore (1) How SnapOPC+ can restore data from several SDVs Depends on the SDV source selection and which data is to be restored to

the original Source Volume



Step 5


Step 3

Step 2

Step 6

Source

1 2 3

1 2 3

1 2 3

1 2 3

1 2 3

SDV1

2

SDV2

2 3

Source

1 2 3

After restoration from SDV1

Source

1 2 3


1 2 3 Source

Source data accessible

after step 6

1


SnapOPC+ Block Restore (1) How SnapOPC+ can restore data from several SDVs SnapOPC+ ensures at all times that each SDV can be used to restore

the Source as it was at the time of the respective Snap



Step 5


Step 3

Step 2

Step 6

Source

1 2 3

1 2 3

1 2 3

1 2 3

1 2 3

SDV1

2

SDV2

2 3 1 2 3


1 2 3 Source

1

Source

1 2


3

Source

1

3

1


SnapOPC+ Read & Write Operations (1) Reading data from the source disk Area to be read is fetched normally directly from the Copy Source


Copy Source Volume

SnapOPC+ Tracker within

CM cache



Application read

G3 G2

G1

Copy Destination Volume Snapshots ETERNUS DX Advanced Copy Functions 33

SnapOPC+ Read & Write Operations (2) Reading data from the Destination Volume Area to be read is checked in the SnapOPC tracker

• Data that has not been changed is taken from the copy source



Application reads unmodified data



G2 G1

SnapOPC+ Tracker

G3 Copy Source

Volume


SnapOPC+ Read & Write Operations (3) Writing data to the Source Volume When data arrives that overwrites a section of the Source Volume

• Old data (here white colored) is copied from source to physical destination • New data (here striped) will be written to copy source • At the end the area is marked as "changed" in SnapOPC Tracker


Copy Source Volume

Application writes SnapOPC+ Tracker



G2 G1

G3

modified

Copy Destination Volume Snapshots ETERNUS DX Advanced Copy Functions 35

SnapOPC+ Read & Write Operations (4) Reading backed up data from the Destination Volume Area to be read is flagged in the SnapOPC tracker

• Data that has been changed is fetched from the physical copy destination SDV


SnapOPC+ Tracker



G2 G1

G3


Application read

modified

Copy Source Volume


SnapOPC+ Read & Write Operations (5) Writing data to Destination Volume Latest data in Copy Source


Application writes



G2 G1

G3


Not modified

Not modified

modified

modified

Copy Source Volume

SnapOPC+ Tracker


SnapOPC+ Read & Write Operations (6) Writing data to Destination Volume Latest data in target SDV


Application writes

G2 G1

G3


Not modified

modified

Copy Source Volume

modified

SnapOPC+ Tracker


SnapOPC+ Read & Write Operations (7) Writing data to Destination Volume Latest data in newer SDV than the target SDV


Application writes

G1

G3


modified

G2

Copy Source Volume

not modified

not modified

modified

modified

SnapOPC+ Tracker


Executing SnapOPC+ Restore (2) To restore from one of the target volumes (SDV) There is no full backup of the source data available with SnapOPC+ All SnapOPC+ sessions can remain active


Session 1

Restore

Session 3

Session 4

S

G1

G2

G3

G4

Session 2 Session 2

Session 3


Executing SnapOPC+ Restore (3) To restore from one of the target volumes (SDV) Manual restore with SnapOPC+ using operating system tools of the

server (File Explorer, copy command etc.)


Source Volume

(read only)

Production server

(read/write) copy

Backup Volume


Introduction to Snap Data Pool

Snap Data Pool Functional Description Snap Data Pool Terminology Snap Data Pool Features Snap Data Pool Configuration Guidelines Setting up SDP in ETERNUS Manager GUI


Snap Data Pool Functional Description Snap Data Pool (SDP) provides additional functionality for

SnapOPC and SnapOPC+ SDP prevents the SnapOPC and SnapOPC+ from failing if the pre-

defined capacity of SDV is exceeded • When SDP is enabled and the SDV exceeds its capacity, additional capacity is

automatically assigned from a pool of volumes SDP is a dynamic volume assignment from a pool of special volumes


Source With Snap Data Pool copy

SDV

New Area

Source

SnapOPC

SnapOPC+

Pool of special volumes

SDP

Capacity full Copy SDV

Access to this SDV is stopped. With SnapOPC+ also the older generations are no longer accessible.

Copy process stops to this SDV.

Copy in progress


Snap Data Pool Terminology (1) Snap Data Pool (SDP) There is one SDP per ETERNUS DX system

• Contains all created SDPVs Is generated automatically as the first SDPV is created Snap Data Pool Volume (SDPV) Type of Volume used only for SDP Automatically added to the SDP by creation of this volume type in an

existing RAID group Each SDPV can have a maximal capacity of 2 TB

• Capacity must be a multiple of the Snap Data Pool Element (SDPE) size Can be created and administrated with the ETERNUS Manager GUI or

CLI


Snap Data Pool Terminology (2) Snap Data Pool Element (SDPE) Capacity unit of an SDPV

• Fixed capacity of 1 GB in DX60, DX80 and DX90 • Can be chosen to be 1 GB, 2 GB or 4 GB in all other ETERNUS DX systems

Come in use when any Copy Destination SDV is about to run out of capacity • SDPEs are supplied from SDP to SDV

to expand the available capacity When a Snap sessions completes

then the used SPDEs (if any) are released back to the SDP


Physical SDV Snap Data Pool

SDPV

SDPE

SDPE

SDPE

Copy source Copy Destination logical SDV

SDPE


Snap Data Pool Features (1) Minimizes the risk of loosing a SnapOPC or SnapOPC+

session caused by running out of capacity If storage capacity runs short in an SDV, additional storage area (SDPE)

is automatically supplied from the SDP It is enough for the System Administrator to ensure that the

overall free SDP capacity is sufficient No longer necessary to check the individual free capacity of each SDV SDP capacity can be increased as needed Single SDP used for all SnapOPC and SnapOPC+ sessions Snap Data Pool is not same as Thin Provisioning (although the

functionality is similar) SDP is only usable for SnapOPC and SnapOPC+ sessions


Snap Data Pool Features (2) SDPVs can be created in any RAID Group using any RAID

level Up to the maximum number of logical Volumes allowed per RAID Group It is recommended that all the SDPVs are created in the same RAID

Group • Anyway, encrypted and non-encrypted in separate RAID Groups

Encrypted and non-encrypted SDV and SDPV can not be mixed Encrypted SDPVs can only supply SDPEs to encrypted SDVs Non-encrypted SDPVs can only supply SDPEs to non-encrypted SDVs

Following functions cannot be used for an SDPV Host Affinity settings LUN mapping LUN Concatenation RAID Migration


SDP Configuration Guidelines (1) Do not calculate the capacity of a Snap Data Volume to be too

small only because a Snap Data pool is available The SDP should only be used for unpredictable capacity needs Each SDV should have a capacity of about 30% to 50% of the Source

Volume capacity Relationship between the number of SnapOPC or SnapOPC+

sessions, SDP capacity and SDPE size If SDP has a capacity of 40 GB and SDPE is set to 4 GB

• When 50 Snap sessions are running and 10 of them require each an extra 1 GB capacity that means 10 SDPEs are supplied • No additional SPDEs can be supplied for the other 40 Snap sessions

• A more appropriate setup for this case might be a 40 GB SDP with a 1 GB SDPE size, allowing a maximal of 40 SDPEs


SDP Configuration Guidelines (2) Recommendations for optimizing system performance If performance of the SnapOPC or SnapOPC+ Copy Source and Copy

Destination Volumes is a consideration, use of SDP is not recommended SDPVs should not be created in a RAID Group containing the logical

volumes (Open Volumes) used for normal operation SDPV RAID Groups should be equally divided between the CMs

• The CPU of the controlling CM for a RAID group is also controlling each SDPV that belong to the same RAID group

• When both encrypted and non-encrypted SDVs are used • The SDPVs of each type must be independently allocated to separate RAID Groups

with different controlling CMs


SDP Configuration Guidelines (3) Recommendations for expanding the SDP If SDP usage exceeds 50%

• Start checking the SDP capacity more frequently and consider expanding the SDP • Encrypted and non-encrypted Volumes must be considered separately

When SDP usage exceeds 70% • The SDP should be expanded immediately

• Like without SDP, otherwise accessing the Snap Data Volumes is at risk • Encrypted and non-encrypted Volumes must be considered separately


Setting up SDP in ETERNUS Mngr GUI Make sure to specify the correct SDPE capacity and

encryption setting Creating the first SDPV automatically starts the SDP All further SDPVs become automatically part of the Snap Data Pool

SDPV capacity must be a multiple of the SDPE size


Please note the screenshots may look different depending on the firmware version. Snapshots ETERNUS DX Advanced Copy Functions 51

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