On 06/05/2010 21:07, Erik Trimble wrote:
VM images contain large quantities of executable files, most of which
compress poorly, if at all.
What data are you basing that generalisation on ?
Look at these simple examples for libc on my OpenSolaris machine:
1.6M /usr/lib/libc.so.1*
636K /tmp/libc.gz
I did the same thing for vim and got pretty much the same result.
It will be different (probably not quite as good) when it is at the ZFS
block level rather than whole file but those to randomly choosen by me
samples say otherwise to your generalisation.
Several people have also found that enabling ZFS compression on their
root datasets is worth while - and those are pretty much the same kind
of content as a VM image of Solaris.
Remember also that unless you are very CPU bound you might actually
improve performance from enabling compression. This isn't new to ZFS,
people (my self included) used to do this back in MS-DOS days with
Stacker and Doublespace.
Also OS images these days have lots of configuration files which tend to
be text based formats and those compress very well.
--
Darren J Moffat
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