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Can I resolve queue depth issue by moving FC links to additional HBA?

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Applies to

  • ONTAP
  • Fibre Channel

Answer

  • FC queue depth is per port not per Host Bus Adapter (HBA) so this approach would not resolve the underlying port issue of SCSI queue exhaustion. 
  • You need to reduce the initiator queue or increase the target queue depth by adding more ports and moving some paths to new ports.  

Example:

  • Each storage HBA port could have a queue depth available of 1945 ( 2048 -5 % for critical SCSI commands ) moving FC link to another HBA port would not change this.
    • This means 32 hosts initiator ports with a queue depth of 64  can access the target port 

Additional Information

NOTE: If receiving an error combined with a performance impact Performance issue with STIO TPD cmd alloc threshold reached handle

Please contact NetApp Technical Support or log into the NetApp Support Site to create a technical case. Reference this article for further assistance.

Alternatively :

  • Consider tune the environment and Hosts Calculate queue depth overview.
  • Consider add additional target ports and FC links 
    • Example: from 2 target ports  per node go to 4 this may alleviate the queue depth pressure on each port.
  • Consider moving the environment to a Storage system / HBA card with increased queue depth support for example 4096 ( - 5 % for critical SCSI commands).
    • Alternatively lower the Host queue depth to meet limits 

To Check queue depth per port:

network fcp adapter show -fields queue-depth
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