IJ34354: PROBLEMS IN PREFETCHING WHEN YOU READ WITH AN IO SIZE THAT IS MULTIPLE OF THE GPFS BLOCKS.

APAR status

• Closed as program error.

Error description

• When an application reads with an IO size that is a
  multiple of the GPFS block, prefetching doesn't
  start until the application issue a second read
  request unless the read starts at the beginning of the
  file or  prefetchAggressiveness is set to
  prefetchOnFirstAccess.   This can cause slow read
  performance when read IO size is very big.
  

Local fix

• Set prefetchAggressiveness configuration to
  prefetchOnFirstAccess or reduce the read IO
  size to the GPFS block size.
  

Problem summary

• When an application reads with an IO size that is a
  multiple of the GPFS block, prefetching doesn't
  start until the application issue a second read
  request unless the read starts at the beginning of the
  file or  prefetchAggressiveness is set to
  prefetchOnFirstAccess.   This can cause slow read
  performance when read IO size is very big.
  

Problem conclusion

• This problem is fixed in 5.0.5  PTF 10
  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:
  Improve read performance with large IO sizes.
  
  Work Around:
  Set prefetchAggressiveness configuration to
  prefetchOnFirstAccess or reduce the read IO
  size to the GPFS block size.
  
  Problem trigger:
  Application issue read with IO size that is
  much bigger than the GPFS block size.
  
  Symptom:
  Performance Impact/Degradation
  
  Platforms affected:
  ALL Operating System environments
  
  Functional Area affected:
  All Scale Users
  
  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