Frank Cusack wrote:
Patrick Bachmann:
Hey Bill,
Bill Sommerfeld wrote:
Overly wide raidz groups seems to be an unfenced hole that people new to
ZFS fall into on a regular basis.
The man page warns against this but that doesn't seem to be sufficient.
Given that zfs has relatively few such traps, perhaps large raidz groups
ought to be implicitly split up absent a "Yes, I want to be stupid"
flag..
IMHO it is sufficient to just document this best-practice.
I disagree. The documentation has to AT LEAST state that more than 9
disks gives poor performance. I did read that raidz should use 3-9 disks
in the docs but it doesn't say WHY, so of course I went ahead and used
12 disks.
When I say I disagree, I mean this has to be documented in the standard
docs (man pages) not some best-practices guide on some wiki.
But really I disagree that this needs documentation. So much of zfs is
meant to be automatic, now we're back to worrying about stripe width?
(Or maybe that's not the problem but it sure is the same type of manual
administration.) I may have 12 disks and it simply does not make sense
(for my theoretical configuration) to split them up into two pools. I
would then have to worry about sizing each pool correctly. zfs is supposed
to fix that problem.
This may just be a matter of wording, but you wouldn't have to split it
up into two pools. You could use two smaller raidz vdevs within the
same pool.
-- Rich.
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