IBM Support

Undetected Data Corruption of Metro or Global Mirror Target Volumes which are stopped with “-access” flag

Flashes (Alerts)


Abstract

If a Metro or Global Mirror target volume that is using a change volume is stopped with the “-access” flag there is a possibility that not all changes will be copied to the target volume when the relationship is restarted. The same issue can also affect Hyperswap.

The "-access" flag is used to make the secondary site volume writeable, and is normally only used during failovers, or some DR tests.

Content

This issue affects both Global Mirror with Change Volumes, as well as Metro or Global Mirror with consistency protection and Hyperswap.  

If the Metro or Global Mirror relationship or consistency group is stopped with the "-access" flag while the change volume is active, the system will not copy all of the necessary changes when the relationship is restarted. This will cause an undetected data loss on the secondary volume.
Since the change volume must be active when the relationship is stopped, systems using Metro or Global Mirror with consistency protection are much less likely to be affected.
Systems using Hyperswap  have the same level of exposure as Metro or Global Mirror with consistency protection, however Hyperswap systems should only run the stop with access command after multiple failures,  This does not affect any of the automated Hyperswap site changes.
Identification of Affected Metro or Global Mirror Relationships

Customers running affected systems who suspect that the "-access" flag may have been used when stopping relationships in the past should perform consistency checking between source and target volumes to determine if any re-synchronisation of data is required.  Contact IBM Support if assistance is required with this activity.
Fix
This issue was introduced in 8.2.1.0 and is fixed under APARs HU02212 in 8.2.1.11 and 8.3.1.2.  Installing the fix on the secondary cluster is sufficient to prevent the fault from reoccurring.
After installing the fix, customers are advised to delete and recreate any affected Metro or Global Mirror relationships to force a full copy.
Mitigation
For systems running 8.2.1 or 8.3 prior to 8.2.1.11 and 8.3.1.2, this issue can be avoided by refraining from using the "-access" flag when stopping Global Mirror with Change Volumes or Metro/Global Mirror with consistency protection relationships.
Future updates
IBM is working on tools to help identify whether the stop with access command has been run, and will update this document with details once they are available.

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Document Information

Modified date:
28 March 2023

UID

ibm16254754

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