IT36921: VSNAP SERVER REPORTS INCORRECT DEDUPLICATION RATIO OF 1.00

APAR status

• Closed as program error.

Error description

• The deduplication ratio reported for a vSnap server can be
  incorrectly shown as 1.00. The value implies that there is no
  deduplication when in reality the vSnap pool does have some
  amount of deduplicated data.
  
  This incorrect value can be seen in the dashboard of the
  IBM Spectrum Protect Plus GUI or in the vSnap Storage
  Utilization
  report.
  It can also be seen from the vSnap CLI by using the command:
  vsnap pool show.
  The issue can be confirmed by examining the output of the "vsnap
  pool show" vSnap command.
  When the vSnap server processes data, it is first compressed and
  then deduplicated.
  On a healthy system, the Initial Data Size is the largest value.
  The Compressed Data Size is smaller, and finally the
  Deduplicated Data Size is even smaller.
  
  For example:
  INITIAL DATA SIZE: 706.59TB
  COMPRESSED DATA SIZE: 263.97TB
  DEDUPLICATED DATA SIZE: 178.69TB
  In case of a healthy system where deduplication is disabled, the
  Deduplicated Data Size is the same as the Compressed Data Size.
  
  In comparison, on systems where an incorrect deduplication ratio
  is seen, it can be observed that the Deduplicated Data Size is
  larger than the Compressed Data Size,
  for example:
  INITIAL DATA SIZE: 113.14TB
  COMPRESSED DATA SIZE: 93.83TB
  DEDUPLICATED DATA SIZE: 96.14TB
  
  The issue occurs because the Deduplicated Data Size is inflated
  as a result of incorrect space accounting
  of evicted entries as described in APAR IT31918.
  As a result, the deduplication ratio is calculated as a value
  that amounts to be less than 1.00 which is an invalid value.
  The vSnap server corrects it to a value of 1.00 which is still
  an inaccurate representation of the actual space usage.
  
  
  | MDVREGR 10.1.4.0  5737SPLUS |
  
  IBM Spectrum Protect Plus Versions Affected:
  IBM Spectrum Protect Plus 10.1.5 and later versions
  
  Initial Impact: Medium
  
  Additional Keywords: SPP, SPPlus, Deduplication, ratio , ZFS,
  TS005184612
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED:                                              *
  * IBM Spectrum Protect Plus level 10.1.5, 10.1.6, 10.1.7 and   *
  * 10.1.8                                                       *
  ****************************************************************
  * PROBLEM DESCRIPTION:                                         *
  * See Error Description                                        *
  ****************************************************************
  * RECOMMENDATION:                                              *
  * Apply fixing level when available. This problem is currently *
  * projected to be fixed in IBM Spectrum Protect Plus level     *
  * 10.1.9. Note that this is subject to change at the           *
  * discretion of IBM.                                           *
  ****************************************************************
  

Problem conclusion

• Implemented code fixes to correct the space accounting of unique
  blocks evicted from the DDT. Any existing discrepancy caused by
  previously evicted blocks cannot be corrected. The fix only
  applies to newly evicted blocks going forward. For existing
  vSnap pools, the fix ensures that any existing discrepancy will
  not grow, but some amount of inaccuracy will remain in the
  reported deduplication ratio. For new vSnap pools, the fix
  ensures that the discrepancy will not occur and the reported
  ratio will be accurate.
  

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:

Modules/Macros

• vSnap    ZFS
  

Fix information

• Fixed component name

  SP PLUS

• Fixed component ID

  5737SPLUS

Applicable component levels