Help me select hardware....Some real world data that might help

[Oliver Fromme]

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.

Best regards
   Oliver

-- 
Oliver Fromme, secnetix GmbH & Co. KG, Marktplatz 29, 85567 Grafing b. M.
Handelsregister: Registergericht Muenchen, HRA 74606,  Geschäftsfuehrung:
secnetix Verwaltungsgesellsch. mbH, Handelsregister: Registergericht Mün-
chen, HRB 125758,  Geschäftsführer: Maik Bachmann, Olaf Erb, Ralf Gebhart

FreeBSD-Dienstleistungen, -Produkte und mehr:  http://www.secnetix.de/bsd

"In My Egoistical Opinion, most people's C programs should be indented
six feet downward and covered with dirt."
        -- Blair P. Houghton