Taking an Incremental FlashCopy of a Global Mirror Change Volume Target Volume May Result in a Data Integrity Issue

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Abstract

When taking an incremental FlashCopy of a target volume in a Global Mirror change volume relationship, some of the data from the Global Mirror change volume target will not be copied to the FlashCopy target volume. This issue affect SAN Volume Controller, Storwize V7000 and Storwize V7000 Unified.

Content

The following diagram will be used to help explain the configuration which is exposed to this issue.


If the incremental FlashCopy map (Q) is started while the Global Mirror change volume relationship (R) is copying data from the local site to the remote site, then FlashCopy will determine what data to copy based on changes to the Global Mirror target volume. However when FlashCopy reads the data to copy it to the FlashCopy target (F), the data will be read from the change volume (E). This is behaving as designed, so that the incremental FlashCopy target (F) contains a consistent copy of data.

If the Global Mirror change volume relationship (R) is copying data from A to D when the incremental FlashCopy map (Q) is started, some of the data from the Global Mirror change volume target (D) will never be copied to the FlashCopy target (F).

Only customers using incremental FlashCopy in combination with Global Mirror change volumes are exposed to this issue.

The software upgrade test utility can be used to verify if your configuration is exposed to this issue. Details of the utility can be found here:

http://www.ibm.com/support/docview.wss?uid=ssg1S4000585

Affected Releases:

The affected releases of SAN Volume Controller and Storwize V7000 are V6.3.0.0 - V6.4.0.2. This issue was resolved in V6.4.0.3 and later.

The affected releases of Storwize V7000 Unified are 1.3.0.0 and later.

Workaround:

There are a number of workarounds available to this problem, which can be applied until the system software has been updated to a version that resolves this issue.

1. Use thin provisioned FlashCopy or regular FlashCopy instead of incremental FlashCopy.


    This can be achieved by deleting the existing FlashCopy map (Q) and creating a new FlashCopy map with the same source and target volume as the original map (D and F). Details for how to create thin provisioned FlashCopy or regular FlashCopy mappings can be found in the product documentation.

2. The following workaround will allow customers to continue to use incremental FlashCopy


    Prior to using this workaround for the first time, it is important to delete the existing incremental FlashCopy map (Q) so that next copy will be a full copy. Then create a new FlashCopy map (Q') with the same source and target volumes (D and F), but do not start the map. This forces a full copy of data so that the FlashCopy target will contain valid data.

    Then use the following steps every time you wish to start the incremental FlashCopy.

    Note: The screenshots and directions below generated on a Storwize V7000 system running V6.4.0. There may be slight differences on other systems.

    • Stop the Global Mirror change volume relationship (R) with the option that allows read and write access to the secondary volume. For a remote copy relationship which is not in a consistency group this can be achieved by right clicking on the remote copy relationship in the GUI and selecting stop. On the confirmation box, tick the "Allow secondary read/write access" checkbox before pressing the button labelled "Stop Relationship". A similar process exists for a remote copy consistency group.


    • Start the incremental FlashCopy map (Q'). There is no need to wait until the FlashCopy has reached 100% copied before restarting the Global Mirror change volumes.
    • Restart the Global Mirror change volume relationship (R). For a remote copy relationship that is not in a consistency group this can be achieved by right clicking on the remote copy relationship in the GUI and selecting stop. In the confirmation box, tick the appropriate primary volume and press Start Relationship. Make sure that you do not unintentionally reverse the direction of the remote copy relationship. If you are at all unsure about which volume is the master and which volume is the auxiliary you can check this by right clicking on the relationship and choosing “Global Mirror Change Volumes”->”Properties (Master)” and “Global Mirror Change Volumes”->”Properties (Auxiliary)”. Data will be copied from the primary volume to the secondary volume.

Fix

This problem has been resolved under APAR IC86059 in the 6.4.0.3 software release for SAN Volume Controller and IBM Storwize V7000.

A fix will also be available for IBM Storwize V7000 Unified in a future release.

Cross reference information
Segment Product Component Platform Version Edition
Disk Storage Systems IBM Storwize V7000 (2076) 6.4 IBM Storwize V7000 6.3, 6.4
Disk Storage Systems IBM Storwize V7000 Unified (2073) IBM Storwize V7000 1.3

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Document information


More support for:

SAN Volume Controller
6.4

Version:

6.3, 6.4

Operating system(s):

SAN Volume Controller

Reference #:

S1004182

Modified date:

2012-09-05

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