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How ONTAP implements SMB crediting

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Applies to

  • ONTAP 9.4 and later
  • SMB2 and higher

Answer

  • In ONTAP 9.4, throttling of SMB credits was implemented via a maximum credits configuration
    • Prior to 9.4, SMB clients were granted as many credits as they requested
    • By default, Cifs servers created with ONTAP 9.4-9.12 grants 128 credits per connection
    • By default, Cifs servers created with ONTAP 9.13+ grants 512 credits per connection
  • Display the current max-credits value:

cluster1::*> set -privilege advanced
cluster1::*> vserver cifs options show -vserver svm1 -fields max-credits

  • Modify max-credits value:

cluster1::*> vserver cifs options modify -vserver svm1 -max-credits 1024

Additional Information

  • Modified credit value will only take effect on new cifs sessions
  • SMB credits determine the number of outstanding simultaneous requests that the client can have on a particular connection.
  • The allowed range is between 2 and 8192
    • Default value (512 and above) typically does not need to be changed unless confirmed to be root cause or vendor states a specific number of credits are needed.
      • Follow client vendor recommendations if it differs from the default
    • While it is possible to set number of credits to 2, there have been reports that some clients start to misbehave with such a low setting
  • Recommendation from Support is to double the amount of credits as needed up to the max value.
  • As documented in this Microsoft Docs page, Performance tuning for SMB file servers, Windows defaults to 512 credits.
  • For assistance with disabling SMB crediting altogether, contact NetApp Technical Support and reference this article.

 

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