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Why await takes so long despite IO not 100%

Discussion in 'Workarounds and Optimization' started by septi, Jan 1, 2013.

  1. septi

    septi Active Member

    Joined:
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    Code:
    Device:         rrqm/s   wrqm/s     r/s     w/s    rkB/s    wkB/s avgrq-sz avgqu-sz   await  svctm  %util
    sda               1.16    11.75    8.22    5.47   424.31    67.92    71.92     2.03  148.44   3.86   5.29
    sdb               0.62   241.42   43.05   73.24   329.01  1259.82    27.33   177.42 1525.33   7.23  84.04
    sdd               0.74   136.35   61.25   41.54   416.38   712.69    21.97   137.75 1338.76   8.21  84.38
    sdc               0.06     0.00    0.05    0.00     0.20     0.00     7.86     0.00    0.81   0.81   0.00
    dm-0              0.00     0.00    9.23   17.01   422.93    67.88    37.41     3.19  121.75   2.01   5.28
    dm-1              0.00     0.00    0.03    0.00     0.11     0.00     8.00     0.00   12.35   3.57   0.01
    dm-2              0.00     0.00    0.05    0.01     0.23     0.03     8.41     0.00    7.35   3.14   0.02
    
    IO is 84% and yet await time is HUGE. I wonder why.

    For comparison, this is the stat for my other server:
    Code:
    Device:         rrqm/s   wrqm/s     r/s     w/s    rkB/s    wkB/s avgrq-sz avgqu-sz   await  svctm  %util
    sda               1.25   604.69   18.44  178.92   388.08  3137.29    35.73     9.33   47.13   4.41  87.13
    dm-0              0.00     0.00    0.81   88.24    22.10   352.94     8.42     7.96   89.36   5.56  49.54
    dm-1              0.00     0.00    0.00    0.00     0.00     0.00     8.00     0.00    6.10   3.47   0.00
    dm-2              0.00     0.00   18.90  696.09   365.95  2784.35     8.81     8.85   12.16   1.21  86.60
    
    The other server has far higher writes, far higher %util and yet have far lower await time.
     
    #1 septi, Jan 1, 2013
    Last edited: Jan 1, 2013
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