Hello,

I have the strange activity on my Linode. The Munin reports shows that there is constant writing to /dev/xvda at the rate of 30Kb/s. The Linode Graphs shows constant DiskIO at 48 Blocks/sec average. The loading is constant.

The CPU utilization shows the similar graph: constant loading 3.5%.

I've tried top and iotop but unable to figure out what is the problem.

Could you please let me know if you have ideas on how to investigate this issue.

Thanks,
Alex

There's usually at least some load on a host, even when idle. The values you mention are like nothing, you shouldn't worry about it.
If you really want to pinpoint it to a specific process, look into iotop.

Also, remember that munin itself will also generate disk IO and CPU

Actually, I'm worried because iotop shows only zeroes almost all the time:

Total DISK READ: 0.00 B/s | Total DISK WRITE: 0.00 B/s
  TID  PRIO  USER     DISK READ  DISK WRITE  SWAPIN     IO>    COMMAND
    1 be/4 root        0.00 B/s    0.00 B/s  0.00 %  0.00 % init [2]
    2 be/4 root        0.00 B/s    0.00 B/s  0.00 %  0.00 % [kthreadd]
    3 be/4 root        0.00 B/s    0.00 B/s  0.00 %  0.00 % [ksoftirqd/0]
    4 be/4 root        0.00 B/s    0.00 B/s  0.00 %  0.00 % [kworker/0:0]
    5 be/0 root        0.00 B/s    0.00 B/s  0.00 %  0.00 % [kworker/0:0H]
    6 be/4 root        0.00 B/s    0.00 B/s  0.00 %  0.00 % [kworker/u:0]
    7 be/0 root        0.00 B/s    0.00 B/s  0.00 %  0.00 % [kworker/u:0H]
    8 rt/4 root        0.00 B/s    0.00 B/s  0.00 %  0.00 % [migration/0]
    9 be/4 root        0.00 B/s    0.00 B/s  0.00 %  0.00 % [rcu_bh]
   10 be/4 root        0.00 B/s    0.00 B/s  0.00 %  0.00 % [rcu_sched]

Somewhere should be these 30Kb/s, but where are they?

You're probably not spotting them, iotop by default refreshes every second or two. Try

iotop -ao

which will only show processes doing disk io and show the accumulated io.

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I've tried this command and after several minutes of waiting it shows me this report:

Total DISK READ: 0.00 B/s | Total DISK WRITE: 0.00 B/s
  TID  PRIO  USER     DISK READ  DISK WRITE  SWAPIN     IO>    COMMAND
 1055 be/4 root          0.00 B    200.00 K  0.00 %  0.00 % [kjournald]
 2339 be/4 root          0.00 B      0.00 B  0.00 %  0.00 % [flush-202:0]
 2047 be/4 nginx         0.00 B     32.00 K  0.00 %  0.00 % nginx: wo~er process

So there is nothing similar to what the linode charts and munin show. Both of them show the constant IO/CPU loading.

Problem closed. I suspect that this loading is generated by Munin itself.