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From Shady Xu <shad...@gmail.com>
Subject Supervisely, RAID0 provides best io performance whereas no RAID the worst
Date Sat, 30 Jul 2016 16:14:23 GMT
Hi,

It's widely known that we should mount disks to different directory without
any RAID configurations because it provides the best io performance.

However, lately I have done some tests with three different configurations
and found this may not be the truth. Below are the configurations and
statistics shown by command 'iostat -x'.

Configuration A: RAID 0 all 12 disks to one directory
Device:         rrqm/s   wrqm/s     r/s     w/s    rkB/s    wkB/s avgrq-sz
avgqu-sz   await r_await w_await  svctm  %util
sdb               0.01     0.59  112.02   65.92 15040.07 15856.86   347.27
    0.32    1.81    2.36    0.86   0.93  16.49

------------------------------------------------------------------------------

Configuration B: No RAID at all
Device:         rrqm/s   wrqm/s     r/s     w/s    rkB/s    wkB/s avgrq-sz
avgqu-sz   await r_await w_await  svctm  %util
sdc               0.01     0.12    2.88    5.23   364.54  1247.10   397.52
    0.76   93.80    9.05  140.42   2.44   1.98
sdg               0.01     0.07    2.39    5.27   328.72  1246.51   410.93
    0.75   97.88   10.93  137.33   2.63   2.02
sdl               0.01     0.07    2.59    5.46   340.61  1299.00   407.00
    0.82  102.18    9.64  146.09   2.55   2.05
sdf               0.01     0.11    2.28    5.02   291.48  1197.00   407.99
    0.72   99.23    9.15  140.12   2.62   1.91
sdb               0.01     0.07    2.69    5.23   334.19  1238.20   396.99
    0.74   93.84    8.10  137.98   2.41   1.91
sde               0.01     0.11    2.81    5.27   376.54  1262.25   405.56
    0.79   97.62   10.96  143.84   2.58   2.08
sdk               0.01     0.12    3.02    5.20   371.92  1244.48   392.93
    0.79   96.07    8.63  146.85   2.48   2.04
sda               0.00     0.07    2.82    5.33   370.06  1260.68   400.52
    0.78   96.09    9.72  141.74   2.49   2.03
sdi               0.01     0.11    3.09    5.30   378.19  1269.98   392.63
    0.78   92.47    5.98  142.88   2.31   1.94
sdj               0.01     0.07    3.04    5.02   365.32  1185.24   385.01
    0.74   92.22    6.31  144.29   2.40   1.93
sdh               0.01     0.07    2.74    5.34   356.22  1264.28   401.06
    0.78   96.81   11.36  140.75   2.55   2.06
sdd               0.01     0.11    2.47    5.39   343.22  1292.23   416.20
    0.76   96.48   10.26  135.96   2.54   1.99

------------------------------------------------------------------------------

Configuration C: RAID 0 each 12 disks to 12 different directories
Device:         rrqm/s   wrqm/s     r/s     w/s    rkB/s    wkB/s avgrq-sz
avgqu-sz   await r_await w_await  svctm  %util
sdd               0.00     0.10    8.88    7.42  1067.65  1761.12   346.94
    0.13    7.94    3.64   13.09   0.46   0.75
sdb               0.00     0.09    8.83    7.52  1066.16  1784.79   348.65
    0.13    8.02    3.75   13.02   0.47   0.76
sdc               0.00     0.10    8.82    7.48  1073.74  1776.02   349.61
    0.13    8.09    3.76   13.19   0.47   0.76
sde               0.00     0.10    8.74    7.46  1060.79  1771.46   349.63
    0.13    7.80    3.53   12.81   0.45   0.73
sdg               0.00     0.10    8.93    7.46  1101.14  1772.73   350.64
    0.13    7.81    3.70   12.71   0.47   0.77
sdf               0.00     0.09    8.75    7.46  1062.06  1772.08   349.73
    0.13    8.03    3.78   13.00   0.46   0.75
sdh               0.00     0.10    9.09    7.45  1114.94  1770.07   348.76
    0.13    7.83    3.69   12.89   0.47   0.77
sdi               0.00     0.10    8.91    7.43  1086.85  1761.30   348.48
    0.13    7.93    3.64   13.07   0.46   0.75
sdj               0.00     0.10    9.04    7.46  1111.32  1768.79   349.15
    0.13    7.79    3.64   12.82   0.46   0.76
sdk               0.00     0.10    9.12    7.51  1122.00  1783.41   349.49
    0.13    7.82    3.72   12.80   0.48   0.79
sdl               0.00     0.10    8.91    7.49  1087.98  1777.77   349.49
    0.13    7.89    3.69   12.89   0.46   0.75
sdm               0.00     0.09    8.97    7.52  1098.82  1787.10   349.95
    0.13    7.96    3.79   12.94   0.47   0.78

It seems the raid 0 all disks to one directory configuration is the one
which provides the best disk performance and the no raid configuration
provides the worst performance. That's a total opposite fact comparing to
the widely known one. Am I doing anything wrong?

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