disk-io: report iops

[NavidSassan]

useful when using openstack disks that have an iops-limitation

[markuslf]

Could be done platform-dependent without any additional tools using

echo "read: io | merge | sectors | ticks, write: io | merges | sectors | ticks, in_flight | io_ticks | time_in_queue"
cat /sys/block/vda/vda*/stat
sleep 7
cat /sys/block/vda/vda*/stat

https://www.kernel.org/doc/Documentation/block/stat.txt

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Or like in https://github.com/sysstat/sysstat measuring tps, from sources in that order: /proc/diskstats, sysfs, /proc/partitions and then /proc/stat.

https://www.kernel.org/doc/Documentation/iostats.txt