Potential DS8700/DS8800 Undetected Data Error on Release 6.2 code during zHPF Format Writes during Recovery with zHPF Format Write feature enabled in z/OS 1.11, z/OS 1.12 or z/OS 1.13

Flash (Alert)


Abstract

When running a zHPF command chain containing format writes (on DS8000 bundles 76.20.x.y or 86.20.x.y), a timing window exists during control unit recovery from a remote CEC failover such that an undetected data error may occur. DS8100s and DS8300s are not exposed to this issue. Users with DS8700 or DS8800 machines below Release 6.2 are not exposed.

Content

If a new zHPF Format Write chain is interrupted by a remote CEC (DS8K Cluster) failover, where the write has successfully been transferred to the control unit and good ending status given, the sectors in cache may not be properly hardened. The host expects the write to be hardened based on the presentation of good ending status. There have been no client reports of this issue, and so far this has only been seen in an IBM test lab.

For z/OS R11 or R12 a customer is exposed if either of these APARs are installed:
• OA34661 that enables Media Manager to exploit R6.2 zHPF.
• OA34672 that enables QSAM/BSAM to exploit R6.2 zHPF and SAM_USE_HPF(YES) is specified in IGDSMSxx PARMLIB member.

All z/OS R13 customers with R6.2 zHPF are exposed since the Media Manager and QSAM/BSAM exploitation is included in the base release.

With Release 6.2 DS8700/DS8800 microcode and the z/OS levels listed above, System z High Performance FICON (zHPF) supports additional workloads using QSAM, BPAM, and BSAM access methods as well as provide improvements for access methods and middle ware that use the Media Manager as an IO driver (examples include PDSE, VSAM, VSAM/RLS, zFS, HFS, DB2, and IMS). The Release 6.2 microcode also provides special improvements for DB2 list prefetch processing. These changes expand the type of applications that can now use zHPF, including applications performing format writes. The zHPF support must be enabled in both the host system and DS8000 in order for the new functions to be allowed.

Mitigation


Customers on z/OS 1.11 or 1.12 should avoid the installation of PTFs for OA34661 and OA34672, until the APARs/DS8000 microcode mentioned in the "Resolution" information are installed.

If these PTFs have been installed, or z/OS 1.13 is installed, customers need to follow the "Resolution" information below at the earliest possible service opportunity.

Resolution

A DS8000 engineering build to add the microcode fix for this issue as well as to turn on a new Read Feature Code bit to indicate the control unit supports zHPF Format Writes is now available in bundles 76.20.90.0 (DS8700) and 86.20.114.0 (DS8800) or higher (e.g. all 76.3x.xx.x (DS8700) and 86.3x.xx.x (DS8800) bundles).

Prior to installing the new microcode, customers must install z/OS APAR: OA39087 (Media Manager). QSAM/BSAM use of zHPF must remain (or be set) disabled as indicated above until fixes for OA38939 and OA39130 (and pre-reqs OA38966 and OA38925) are also installed. ++ APARs are available from the Support Center.

Cross reference information
Segment Product Component Platform Version Edition
Disk Storage Systems System Storage DS8700 Not Applicable z/OS 6.2 N/A

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Document information


More support for:

System Storage DS8800

Version:

6.2

Operating system(s):

z/OS

Software edition:

N/A

Reference #:

S1004024

Modified date:

2014-01-23

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