ZFS on Linux (Ubuntu) – arcstat.py is now available! How do you run it?

UPDATE: This information is now out of date, see new post here.


One very handy ZFS-related command which has been missing from the standard ZFS on Linux implementation has been arcstat.py. This script provides a great deal of useful information about how effective your adaptive read cache (ARC) is.


ZFSoL 0.6.2 includes it, which you can now update to in Ubuntu with apt-get upgrade. But how do you actually use it when you upgrade? Easy. Assuming you have python installed, run the following (this works for 13.04 at least – we will check the others and update when we do):




This will provide you with the default readout, e.g. for our system which just rebooted:


    time  read  miss  miss%  dmis  dm%  pmis  pm%  mmis  mm%  arcsz     c

21:33:13     3     1         33          1       33        0        0           1        33       2.5G   15G


As you can see, since the system has just rebooted and hasn’t started caching requests the ARC size is quite small – 2.5G.

This is an extremely useful tool to get an idea of how your ARC is performing – we will do a piece on interpreting the results soon!



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