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QoS throughput floor is not met on workloads with low concurrency and low latency

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Category:
ontap-9
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perf
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Applies to

  • ONTAP 9
  • QoS throughput floor (Qos Min)
  • QoS throughput ceiling (QoS Max)

Issue

  • Non-shared QoS Policy with throughput floor (QoS Min) is set on a group of volumes with critical workloads 
  • Non-shared QoS Policy with throughput ceiling (QoS Max) is set on another group of volumes with non-critical workloads
  • When workloads are added to both groups of volumes:
    • QoS Min is set to 10k/s on the critical volumes, but they can only achieve 6k/s (QoS Min is not met) with the following signatures:
      • Extremely low latency (confirmed using qos statistics volume performance show)
        Example:
        cluster::> qos statistics volume performance show -volume vol1 -vserver svm1
        Workload            ID     IOPS       Throughput    Latency
        --------------- ------ -------- ---------------- ----------
        vol1-1354         1354        0            0KB/s        0ms
         
      • Extremely low concurrency (confirmed using qos statistics volume characteristics show)
        Example:
        cluster::> qos statistics volume characteristics show -volume vol1 -vserver svm1
        Workload            ID     IOPS       Throughput Request Size Read Concurrency
        --------------- ------ -------- ---------------- ------------ ---- -----------
        vol1-1354         1354        0            0KB/s           0B   0%           0
         
    • QoS Max is set to 4k/s on the non-critical workloads, they all reach 4k/s with low latency
      • No delay from QoS Min in workload latency beakdown

 

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