[CentOS] Disk read io very high, but no process perform io read

Fri Mar 5 08:33:15 UTC 2021
Simon Matter <simon.matter at invoca.ch>


> We have experienced a very weird problem. The load of the server machine
> is very high. We use "pidstat" and find that the disk read io is very
> high.

If disk read IO is very high, what does it read and what generates the reads?


> But the processes running on this server do not perform any disk read
> operation.
> We also noticed that when we execute "top" command, for most of processes,
> the values in "SHR" column are zero.
> Compared with other normal servers, we found that by executing "free -m",
> the result shows that the buff/cache value in this server is lower than
> the value of other normal servers.
> We also found that there were lots of major page faults by executing "ps
> -o majflt,minflt".
> Swap is not enabled on this server. What could be the reason for this
> issue?
> The centos version:CentOS Linux release 7.3.1611
> kernel version:3.10.0-693.21.1.std7a.el7.0.x86_64
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