Our server occasionally becomes laggy when writing files. using iostat I noticed that the disk utilization is abnormally high. However, the read/write per second does not seem too high

# example output from `iostat -ydx sdb 1`

Device            r/s     w/s     rkB/s     wkB/s   rrqm/s   wrqm/s  %rrqm  %wrqm r_await w_await aqu-sz rareq-sz wareq-sz  svctm  %util
sdb             89.00   69.00   2404.00   2892.00     0.00    14.00   0.00  16.87  152.27 1734.67 320.72    27.01    41.91   6.33 100.00

What could be the cause of this phenomenon?

  • 1
    Is it HDD or SSD? May 3 at 18:05
  • @batistuta09 a HDD, yet i think even HDD should not have that low io speed?
    – ZeroRin
    May 5 at 3:54

1 Answer 1


We see 89 reads per second and 69 writes per second, 158 IOPS. That's great value for HDD (anything more than 100 would be good) and it looks like this is fast HDD (maybe, SAS, maybe, 10K RPM); some (think WD Green) only can do around 40!

Yes, rotating rust is that slow. Bear with it.

  • ah so it's like too much random accesses that causes the problem instead of the total kb, I see, thanks
    – ZeroRin
    May 16 at 3:14
  • Exactly. Your iostat looks like it's random accesses. May 16 at 4:42

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