In discussing storage today we got asked ... / 2012-09-25

2012-09-25 In discussing storage today we got asked ... 6 years ago
In discussing storage today we got asked how many I/O operations per second (IOPS) we see. An interesting question, but how do you measure this. One google search later the answer is easy: iostat as explained at Measuring Disk Usage In Linux (%iowait vs IOPS). First answer from iostat is average since boot, answers after that (given interval and count) are for the measured interval. A sample from the home server greenblatt:
koos@greenblatt:~$ iostat 60 2
Linux 2.6.24-31-server (greenblatt)     09/25/2012

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           3.37    0.01    1.95    0.49    0.00   94.19

Device:            tps   Blk_read/s   Blk_wrtn/s   Blk_read   Blk_wrtn
sda               9.01        87.69       113.18 1181728477 1525265504
sdb               0.96       122.82        98.99 1655093714 1334086098
sdc               0.28         2.29        34.46   30809884  464336050
dm-0              0.52        39.04         1.27  526178078   17057856
dm-1             14.35        84.95        98.70 1144861524 1330106690

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           0.78    0.00    2.86    0.22    0.00   96.14

Device:            tps   Blk_read/s   Blk_wrtn/s   Blk_read   Blk_wrtn
sda               7.87        16.40        98.93        984       5936
sdb               0.00         0.00         0.00          0          0
sdc               0.00         0.00         0.00          0          0
dm-0              0.00         0.00         0.00          0          0
dm-1              0.00         0.00         0.00          0          0
To resolve the dm- names, list the device files in /dev/mapper:
koos@greenblatt:~$ ls -l /dev/mapper
total 0
crw-rw---- 1 root root  10, 63 2012-04-22 20:58 control
brw-rw---- 1 root disk 254,  0 2012-09-23 12:41 vgsw-camera
brw-rw---- 1 root disk 254,  1 2012-09-25 16:22 vgsw-scratch
Which shows that dm-0 is the /dev/mapper/vgsw-camera filesystem.

This will help us get an idea how many iops systems have in our setup.

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