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High latency from SM Sync on SnapMirror Sync(SM-S) primary volumes

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ontap-9
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perf
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Applies to

  • ONTAP 9.9 and earlier
  • SnapMirror Synchronous (SM-S)

Issue

  • High latency from SM Sync on SM-S primary volumes.
  • The high latency could be observed from several different performance monitoring tools, including:
    • CLI
    • OCUM
    • Harvest/Grafana
    • NAbox
  • The high latency from SM Sync in Workload Latency Breakdown could be much higher(in the range of hundres of seconds) than the total Latency in some cases, which clearly indicates a miscalculation.
  • High latency seen when Cloud insights WorkLoad Security is turned on for the volume.
  • The high latency is usually observed when the IOPS is extremely low.

CLI Example:

cluster1::> qos statistics workload latency show -workload vol1-wid26127
Workload        ID    Latency    Network    Cluster    Data    Disk    QoS    NVRAM    Cloud    FlexCache    SM Sync
-----------    -----  ------     ------     ------     ------  ------  ------ ------   ------   ------       ------
vol1-wid26127  26127  991ms      0.1ms      0ms        0.5ms   1.3ms   0ms    0.2ms    0ms      0ms          35s
vol1-wid26127  26127  918ms      0.2ms      0ms        0.8ms   1.1ms   0ms    0.1ms    0ms      0ms          111s

 

 

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