IJ25754: POSSIBLE QUOTA SHARES LOSS (IN-DOUBTS) WHEN THE SOFT LIMIT IS EXCEEDED

APAR status

• Closed as program error.

Error description

• Problem description in customer terms:
  Quota clients request quota
  shares based on the workload
  and in most of the time the
  quota shares given to an active
  client is much bigger than the
  previously pre-defined amount
  (e.g. 20 file system blocks).
  The unused or excess quota shares
  are returned to the quota manager periodically.
  
  At the quota manager side,
  when the quota usage exceeds
  the established soft quota limits,
  the grace period is triggered.
  At this event, the quota shares
  are reclaimed and the quota share
  distribution falls back to a more
  conservative fashion (based on
  predetermined amount).
  
  In certain workloads, when the
  partial quota shares are returned
  to the manager along with the usage
  updates and as a result it triggers
  the soft quota limit exceeded event,
  some amount of quota shares are
  lost due to mismanagement of
  quota shares between the client
  and the manager, leading to
  permanent loss of quota shares correctable
  via the mmcheckquota command.
  

Local fix

• None. Establishing soft quota limits
  such that the usage is less
  likely to trigger repeatedly the
  "soft quota limit exceeded" events minimizes
  the timing window of hitting this issue.
  

Problem summary

• Problem description in customer terms:
  Quota clients request quota
  shares based on the workload
  and in most of the time the
  quota shares given to an active
  client is much bigger than the
  previously pre-defined amount
  (e.g. 20 file system blocks).
  The unused or excess quota shares
  are returned to the quota manager periodically.
  
  At the quota manager side,
  when the quota usage exceeds
  the established soft quota limits,
  the grace period is triggered.
  At this event, the quota shares
  are reclaimed and the quota share
  distribution falls back to a more
  conservative fashion (based on
  predetermined amount).
  
  In certain workloads, when the
  partial quota shares are returned
  to the manager along with the usage
  updates and as a result it triggers
  the soft quota limit exceeded event,
  some amount of quota shares are
  lost due to mismanagement of
  quota shares between the client
  and the manager, leading to
  permanent loss of quota shares correctable
  via the mmcheckquota command.
  

Problem conclusion

• Benefits of the solution, in customer terms:
  Avoid quota share loss in workloads
  that have frequent quota usage
  floating below and above the
  pre-established soft quota limits.
  
  Work Around:
  None. Establishing soft quota limits
  such that the usage is less
  likely to trigger repeatedly the
  "soft quota limit exceeded" events minimizes
  the timing window of hitting this issue.
  
  Problem trigger:
  Timing and workload specific caused
  by when the quota usage exceeds
  the soft limits.
  
  Symptom:
  Quota shares loss, thus increasing the
  in-doubt values, caused by the soft quota
  exceeded events.  The loss of shares can't be
  reclaimed without running the
  mmcheckquota command.
  
  Platforms affected:
  
      ALL Operating System environments
  
  Functional Area affected:
  Quotas
  
  Customer Impact:
  
  High Importance: an issue which will cause a
  degradation of the system in some manner, or
  loss of a less central capability
  

Temporary fix

Comments

APAR Information

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

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

Fix information

• Fixed component name

  SPEC SCALE STD

• Fixed component ID

  5737F33AP

Applicable component levels