[closed] Identifying disk reader/writer

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.

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.