Help me select hardware....Some real world data that might help
olli at lurza.secnetix.de
Thu Jan 29 06:48:57 PST 2009
Paul Tice wrote:
> I just bumped up the kmem, arc.max, enabled zil and reenabled
> mdcomp. Prefetch is disabled. Less than 1 minute into a backup
> run of only 4 machines, I've got a fresh ZFS wedgie.
How exactly did you bump up kmem? As far as I know, it
is not necessary anymore on 8-current/amd64, because the
defaults are already much larger. In fact it might be
possible that your tuning made things worse.
> As I understand it, the ZIL is not as much of an integrity boost as
> a speed boost, especially since we already have checksum-per-block.
The checksum feature works purely on a block level, while
the intent log (ZIL) records certain changes to meta data
on the file system, similar to a journal, which can be
used for recovery after a crash (power outage, hardware
failure, kernel panic, human error). Both features are
completely orthogonal, one cannot replace the other.
Therefore I recommend to keep the ZIL enabled.
Oliver Fromme, secnetix GmbH & Co. KG, Marktplatz 29, 85567 Grafing b. M.
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