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Higher read I/O latency with some bursty workloads

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Category:
ontap-9
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perf
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Applies to

  • ONTAP 9
  • AFF systems

Issue

  • The system is experiencing higher read I/O latency in LUNs or volumes
    • We can see that in a Grafana or any other reporting tool for Backend Read Latency monitoring. 
  • That high read I/O latency is specially noticed in drives
    • But it can be pointing to Network/Protoco, like FCP.
  • The latency spikes are above 15ms, which is higher than the expected normal latency. Example:

::> qos statistics volume latency show -volume <vol_name> -vserver <SVM_name>
Workload     ID     Latency     Network       Cluster     Data          Disk      ...
--------     --     -------     ---------     -------     ---------     -------   ...
-total-       -     17.47ms     1018.00us     0ms            2.04ms     14.41ms   ...
-total-       -      4.43ms     1400.00us     0ms          861.00us      2.17ms   ...
-total-       -     16.98ms      133.00us     0ms            1.93ms     14.92ms   ...
-total-       -      7.49ms      748.00us     0ms         1199.00us      5.54ms   ...
-total-       -     12.77ms      207.00us     0ms         1496.00us     11.06ms   ...
-total-       -     10.02ms      227.00us     0ms            2.03ms      7.76ms   ...
...             

 

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