Yes you are. 

If you loose any one of your disks with a raid 0 spanning all drive you will loose all the data in that directory. 

And disks do die. 

Yes you get better single threaded performance but are putting that entire directory/data set at higher risk

Cheers

On Saturday, July 30, 2016, Shady Xu <shadyxu@gmail.com> wrote:
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?