falidae# iostat

Linux 3.12-0.bpo.1-amd64 (falidae)      30/08/14        _x86_64_        (8 CPU)

avg-cpu:  %user   %nice %system %iowait  %steal   %idle

           1.29    0.04    0.26   19.77    0.00   78.65

Device:            tps    kB_read/s    kB_wrtn/s    kB_read    kB_wrtn

sda              34.12       637.80       218.87     640881     219924

sdc              21.07        87.49       403.81      87910     405759

sdb              90.41       591.97       403.81     594830     405759

md0             132.01       677.53       403.67     680806     405620

dm-0              0.09         0.37         0.00        372          0

scd0              0.02         0.10         0.00         96          0

dm-1            130.91       674.30       403.66     677557     405608

dm-2              0.33         1.31         0.01       1317         12

dm-3              0.09         0.37         0.00        376          0

dm-4              0.09         0.37         0.00        372          0

dm-5              0.09         0.37         0.00        372          0

19.77% seems very high for what appeared to be a idle system running X-Windows and two idle web browsers. Any ideas on how to find what is causing it to be so high?

(in the above, sda is solid state disk used by /, sdb+sdc is the underlying disk used by md0 which is raid1)

Is dropping a bit now, but still high:

Also considered the possibility that md0 is resyncing - that would explain everything. Unfortunately /proc/mdstat says it isn't.