ZFS/compression/performance

[Bob Friesenhahn]

On Wed, 12 Oct 2011, Jeremy Chadwick wrote:
>
> That might be the case on OpenSolaris but the performance hit on
> FreeBSD RELENG_8 is very high -- enough that enabling compression (using
> the defaults) causes stalls when I/O occurs (easily noticeable across
> SSH; characters are delayed/stalled (not buffered)), etc..

Solaris solved the problem by putting the zfs writer threads into a 
special scheduling class so that they are usually lower priority than 
normal processing.  Before this change, a desktop system would become 
almost unusable (intermittent loss of keyboard/mouse) while writing 
lots of data with compression enabled.  Some NFS servers encountered 
severe enough issues that NFS clients reported NFS timeouts.

> Another point: I haven't tinkered with compression on our Solaris 10
> machines at work so I don't know if it performs better, equal, or worse
> than FreeBSD or OpenSolaris.

>From what you describe, Solaris must be doing much better in this 
regard than FreeBSD.  Solaris is not necessarily faster but there is 
now little impact on interactive tasks.

Bob
-- 
Bob Friesenhahn
bfriesen at simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/