slow ZFS on FreeBSD 8.1

Peter Jeremy peterjeremy at acm.org
Sat Jan 1 00:00:31 UTC 2011


On 2010-Dec-30 02:31:30 -0500, Adam Stylinski <kungfujesus06 at gmail.com> wrote:
>I can tell you what the problem is right now, actually.  ZFS performs
>very poorly on low performance CPUs (i.e. your Atom N330).

I would disagree.  In this case, the op's most serious problem is a
bug in
sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c:arc_memory_throttle()
which is leading to ARC starvation.  The direct effect of this is very
poor ZFS I/O performance.  It can be identified by very high "inactive"
and possibly "cache" memory (as reported by 'systat -v' or top) as well
as very high kstat.zfs.misc.arcstats.memory_throttle_count

This bug was fixed in r210427 on -current, r211599 on 8.x and
r211623 on 7.x.

>  Try the
>same system with a different CPU and you'll get a different result.

Not until the above bug is fixed.

That said, ZFS is far more CPU intensive than UFS and a more powerful
CPU may help - especially if you want gzip compression and/or sha256
checksumming.

-- 
Peter Jeremy
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