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CONTAP-72312: Applications experience latency due to a single slow SSD

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Issue

  • Applications experience latency due to a single slow SSD
  • The Slow SSD is confirmed from ONTAP side with performance commands such as [statit]
  • EMS.log when disk is slow:
    [ [node1: scsi_cmdblk_strthr_admin: scsi.cmd.checkCondition:error]: Disk device 0c.01.1: Check Condition: CDB 0x8a:000000019b222800:00000120: Sense Data SCSI:aborted command - (0xb - 0x2f 0x14 0x0)(4509).]
  • EMS.log short time later when disk recovers:
    [ [node1: scsi_cmdblk_strthr_admin: scsi.cmd.retrySuccess:debug]: Disk device 0c.01.1: request successful after retry #0/#1: cdb 0x8a:000000019b222800:00000120 (5017).]
  • The [statit] output shows the last disk 0c.01.5 having higher latency:
    [node> statit -e
    Disk Statistics (per second)
    ut% is the percent of time the disk was busy.
    xfers is the number of data-transfer commands issued per second.
    xfers = ureads + writes + cpreads + greads + gwrites
    chain is the average number of 4K blocks per command.
    usecs is the average disk round-trip time per 4K block.
    disk ut% xfers ureads--chain-usecs writes--chain-usecs cpreads-chain-usecs greads--chain-usecs gwrites-chain-usecs
    /aggr1/plex0/rg0:

0a.00.9 2 275.84 0.00 .... . 95.38 36.71 32 180.46 18.28 41 0.00 .... . 0.00 .... .
0a.00.1 2 276.54 0.50 1.40 120 95.88 36.57 31 180.16 18.30 40 0.00 .... . 0.00 .... .
0a.00.3 1 2659.57 2030.59 3.70 131 266.35 7.80 89 362.63 2.86 210 0.00 .... . 0.00 .... .
3d.00.4 1 2667.07 2047.99 3.79 112 261.65 8.27 56 357.43 2.93 143 0.00 .... . 0.00 .... .
0a.00.5 1 2733.05 2096.08 3.72 108 271.35 8.25 89 365.63 2.95 153 0.00 .... . 0.00 .... .
3d.00.6 1 2506.70 1916.42 3.43 124 243.45 8.19 66 346.83 2.85 146 0.00 .... . 0.00 .... .
0a.00.7 1 2450.61 1897.82 3.47 109 224.46 8.40 84 328.33 2.84 150 0.00 .... . 0.00 .... .
3d.00.8 1 2462.91 1902.72 3.58 117 228.55 8.35 69 331.63 2.89 149 0.00 .... . 0.00 .... .
3d.00.10 1 2500.00 1913.12 3.45 117 238.25 7.96 78 348.63 2.76 152 0.00 .... . 0.00 .... .
3d.00.2 1 2428.81 1839.93 3.54 117 243.75 7.98 88 345.13 2.92 149 0.00 .... . 0.00 .... .
3d.00.0 1 2451.11 1877.52 3.44 120 237.35 8.17 97 336.23 2.89 153 0.00 .... . 0.00 .... .
0c.01.5 95 2352.92 1538.77 6.53 2579 385.19 12.08 2353 428.96 3.56 2176 0.00 .... . 0.00 .... .]

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