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SAN increased latency with low throughput from VAAI Copy Offload

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Category:
ontap-9
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perf
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Applies to

  • ONTAP 9
  • VAAI Copy Offload
  • Data ONTAP 8 7-Mode

Issue

  • System Manager dashboard displays a high LUN latency without a significant increase in IOPS or throughput.
  • High latency is mostly with SAN Other operations. 
  • HDD read/write or SSD read/write is much higher than FCP in/out or iSCSI in/out from the sysstat -x outputs. 
    • If VAAI Copy Offload source volume and destination volume are from the same node, Net in/out is as low as FCP in/out or iSCSI in/out in sysstat -x.
    • If VAAI Copy Offload source volume and destination volume are from different nodes, Net in/out is as high as HDD read/write or SSD read/write in sysstat -x.

Example 1: 

System Manager dashboard displays a high LUN latency

Notes:

  • iSCSI + HDD
  • VAAI Copy Offload Source volume and Destination volume on the same node
  • Net in/out & iSCSI in/out are both much lower than HDD read/write

Example 2:

System Manager dashboard displays a high LUN latency

Notes: 

  • FCP + SSD
  • Source volume and Destination volume are from different nodes
  • This is the Source node
  • Net out is as high as SSD read, and they are both much higher than FCP out

Example 3: 

SAN increased latency with low throughput from VAAI Copy Offload

Notes:

  • FCP + SSD
  • Source volume and Destination volume are from different nodes
  • This is the Destination node
  • Net in is as high as SSD write, and they are both much higher than FCP in

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