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Disk latency with extCache.io.writeError and insert_reject_throttle_io

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ontap-9
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perf
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Applies to

  • ONTAP 9
  • All FAS systems with NVMe based Flash Cache

Issue

  • Increased latency on Disk Delay Center
cluster01::> qos statistics volume latency show -vserver vserver01 -volume volume01
Workload            ID    Latency    Network    Cluster       Data       Disk    QoS Max    QoS Min      NVRAM      Cloud  FlexCache    SM Sync         VA
--------------- ------ ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ----------
-total-              -    24.06ms   104.00us    53.00us   556.00us    23.35ms        0ms        0ms     3.00us        0ms        0ms        0ms        0ms
volume01-wid51230     51230    22.49ms   104.00us    52.00us   526.00us    21.81ms        0ms        0ms     3.00us        0ms        0ms        0ms        0ms
-total-              -    13.60ms   143.00us    60.00us   188.00us    13.21ms        0ms        0ms     2.00us        0ms        0ms        0ms        0ms
volume01-wid51230     51230    13.19ms   143.00us    59.00us   185.00us    12.80ms        0ms        0ms     2.00us        0ms        0ms        0ms        0ms
  • Multiple events
wafl_exempt09: ems.engine.suppressed:debug]: Event 'extCache.io.writeError' suppressed 67626 times in last 601 seconds.
wafl_exempt09: extCache.io.writeError:notice]: WAFL external cache I/O write error: Insertq_save: unable to set up context chain, code 0
  • FlashCache no longer inserts
cluster01::> node run -node node02 stats show -p flexscale-access
Cache                                               Reads       Writes      Disk Reads
Usage    Hit   Meta   Miss Hit Evict Inval Insert Chain Blocks Chain Blocks  Replaced
%     /s     /s     /s   %    /s    /s     /s    /s     /s    /s     /s        /s
45    703     11  39171   1     0     0      0     0      0     0      0       109
45    320     26  37607   0     0     0      0     0      0     0      0        98
45    903     51  38018   2     0     0      0     0      0     0      0       114
  • Reboot fixes it temporarily

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