IZ91233: EXTRA CLEAR ACA SENT WHILE USING ROUND ROBIN ALGORITHM APPLIES TO AIX 5300-10

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• When using the round robin MPIO algorithm, the SCSI disk head
  driver may send out extraneous Clear ACA task management
  commands.  Most storage devices just accept and ignore such
  extra commands.  But if a storage device rejects the extra
  clear ACA (as it is allowed to do per the standards), this
  could result in extra LUN or Target reset commands, which
  could affect I/O throughput.
  

Local fix

Problem summary

• When using the round robin MPIO algorithm, the SCSI disk head
  driver may send out extraneous Clear ACA task management
  commands.  Most storage devices just accept and ignore such
  extra commands.  But if a storage device rejects the extra
  clear ACA (as it is allowed to do per the standards), this
  could result in extra LUN or Target reset commands, which
  could affect I/O throughput.
  

Problem conclusion

• Modified the SCSI disk head driver to close a timing window
  that caused the head driver to send multiple Clear ACA
  task management functions for a single check condition.
  

Temporary fix

Comments

• 5300-10 - use AIX APAR IZ91233
  5300-11 - use AIX APAR IZ91151
  5300-12 - use AIX APAR IZ90693
  6100-03 - use AIX APAR IZ93673
  6100-04 - use AIX APAR IZ93601
  6100-05 - use AIX APAR IZ93420
  6100-06 - use AIX APAR IZ93005
  6100-06 - use AIX APAR IZ85136
  7100-00 - use AIX APAR IZ85504
  

APAR Information

• APAR is sysrouted FROM one or more of the following:

  IZ85136

• APAR is sysrouted TO one or more of the following:

Fix information

• Fixed component name

  AIX 5.3

• Fixed component ID

  5765G0300

Applicable component levels

• R530 PSY U838237

     UP11/02/23 I 1000

PTF to Fileset Mapping

• U838237 devices.fcp.disk.rte 5.3.10.5