In certain circumstances, CKD (zOS) host writes to a FlashCopy Target in conjunction with uncorrectable SAN link errors can result in repetitive microcode logic errors
and possible loss of access to the DS8700/DS8800.
The issue specifically requires a combination of CKD writes to a FlashCopy Target volume in addition to uncorrectable SAN link errors. Most notable use for a zOS
Host to write to a FlashCopy Target is during disaster recovery testing in a Global Mirror (GM) or Metro Global Mirror (MGM) environment. Typically, for disaster
recovery tests, at the Global Mirror secondary, a practice copy will be created from the consistent copy of the data. This practice copy is then made available for
Host I/O directly to it.
Another common use for a FlashCopy target, tape backup, is not affected by this issue as tape backup only does Host reads and not writes.
Release 6.1, Release 6.2 (prior to Service Pack 2.1), Release 6.3 (prior to Service Pack 1) on the DS8700 and DS8800 platforms are affected.
Two aspects of mitigation for this problem:
1. Avoid any activity which involves CKD I/O to a FlashCopy Target. Avoid disaster recovery testing in Global Mirror environments which involve using a practice
copy from the Global Mirror target until fix is delivered.
2. In the case of an actual disaster where the Global Mirror primary site is no longer available, the user can invoke a fast reverse restore from the consistent copy
(D volume) of the data back to the C volume and run the zOS host specifically to the C volume. The C volume in this example is not a FlashCopy target, it is a
Note: If the application waits for the background copy to complete prior to initiating other CKD writes to the FlashCopy Target volume, there is no risk of the abort mentioned above.
A fix has been available in microcode bundles 18.104.22.168 or higher for DS8700s and in 22.214.171.124 or higher for DS8800s. A fix is also now available in release 6.3 microcode bundles 126.96.36.199 or higher for DS8700s and in 188.8.131.52 or higher for DS8800s.
|Disk Storage Systems||System Storage DS8700||Not Applicable||z/OS||N/A|
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