[linux-lvm] dmioscope: visualise IO distribution for DM devices

[Bryn M. Reeves]

I wanted to give a quick plug for a little tool I've been working on for
the last few weeks: dmioscope is a python script that uses device-mapper
statistics to generate histograms of IO distribution on a DM device:

# python dmioscope.py -C READS -b 6 3 0 vg_hex/root
Initialised READS adaptive histogram with 6 bins,
min_size=1677721.
vg_hex/root: current IO distribution
0.0 2000.0 4000.0 6000.0 8000.0
+-------------------------------------------------------------
0.0B |#######
5.3GiB |#####################################################
10.7GiB |#####
16.0GiB |###
21.3GiB |
26.7GiB |
90.00% of IO reaches 50.00% of disk.
[...]

(watch reads, six bins, interval of 3s, carry on forever)

It's useful for finding and tracking hot-spots in real time, and for
getting a general picture of where IO is going to on a device. I'm
hoping it can also be used to get an idea of the benefits that can
be achieved with caching.

I've pushed it to GitHub - if anyone finds any bugs, or has any
suggestions, I'm very interested to hear them: there's a README.md with
usage information and more details on the histogram implementation on
the main page:

https://github.com/bmr-cymru/dmioscope

Regards,
Bryn.