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Saurabh Nanda
Asked: 2019-01-29 02:44:25 +0800 CST

Difference in utilisation reported by iostat for two identical disks in RAID1

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I'm trying to debug some weird behaviour with Postgres performance and am trying to understand the iostat output. I'm on 2x SSD on RAID1. Why would one of the disks be reported at ~21% utilisation and the other at ~95% utilisation? Shouldn't they be exactly the same?

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avg-cpu:  %user   %nice %system %iowait  %steal   %idle
          10.03    0.00    5.28    1.24    0.00   83.45

Device            r/s     w/s     rMB/s     wMB/s   rrqm/s   wrqm/s  %rrqm  %wrqm r_await w_await aqu-sz rareq-sz wareq-sz  svctm  %util
loop0            0.00    0.00      0.00      0.00     0.00     0.00   0.00   0.00    0.00    0.00   0.00     0.00     0.00   0.00   0.00
sda             83.20  493.60      0.72      8.11     0.00     1.80   0.00   0.36    0.56    0.39   0.24     8.83    16.83   0.37  21.36
sdb             24.40  493.60      0.24      8.11     0.00     1.80   0.00   0.36    3.41    1.91   1.02    10.10    16.83   1.82  94.24
md0              0.00    0.00      0.00      0.00     0.00     0.00   0.00   0.00    0.00    0.00   0.00     0.00     0.00   0.00   0.00
md1              0.00    0.00      0.00      0.00     0.00     0.00   0.00   0.00    0.00    0.00   0.00     0.00     0.00   0.00   0.00
md2            107.60  494.60      0.96      8.12     0.00     0.00   0.00   0.00    0.00    0.00   0.00     9.12    16.81   0.00   0.00
linux

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