IJ41211: UNEXPECTED READ-DRIVEN CACHING BEHAVIOR FOR AFM COS

APAR status

• Closed as program error.

Error description

• When afmPrefetchThreshold is set to the default value of
  0 for an AFM cloud object storage (COS) fileset, a file
  is
  not fully prefetched after any three random blocks of the
  file are read.
  

Local fix

Problem summary

• Objects are not fully prefetched
  at the Cache on reading 4th block
  when afmPrefetchThreshold is set to 0,
  and io pattern is random.
  

Problem conclusion

• This problem is fixed in 5.1.2 PTF 6
  To see all Spectrum Scale APARs and
  their respective fix solutions refer to page
  https://public.dhe.ibm.com/storage/spectrumscale/spectrum_scale
  apars.html
  
  Benefits of the solution:
  Objects get prefetched fully
  at cache (in the background) upon
  reading the 4th block at cache
  in any order (random or sequential).
  
  Work Around:
  Read 4 blocks sequentially as compared to random
  Problem trigger :
  1. In RO/LU/IW/SW mode of operation,
  with AFM COS as the backend
  have an uncached file
  (evict file in case of SW or IW from cache)
  2. Read 4 data blocks randomly on the file
  at cache.. (make sure no
  2 blocks are read sequentially)
  Symptom:   Unexpected Behavior
  Platforms affected:  Linux Only (AFM Gateway nodes)
  Functional Area affected: AFM
  Customer Impact: High Importance
  

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