28.01.2013 09:03, Steve O'Hara-Smith:
On Sun, 27 Jan 2013 22:05:05 -0800
Michael Sierchio <ku...@tenebras.com> wrote:
On Sun, Jan 27, 2013 at 5:36 PM, Shane Ambler <free...@shaneware.biz>
wrote:
I recall reading that using partitions for zfs on FreeBSD was as good as
full disks.
No, it isn't - ZFS can fully utilize disk caches when presented with
whole devices. There are possible reasons to create partitions - one
being that if an unfriendly OS sees the device, it won't try to
initialize it if it sees a partition map. Another is using a cheap
RAID controller that can't be fully disabled - in which case you
generally need to create a partition that doesn't include the last few
sectors of the disk, where such controllers keep magic data.
There's one other good reason to use partitions when mirroring.
When the time comes to replace a drive in a mirror it is necessary that the
new drive be the same size (or larger) than the one it replaces. Given that
drives of nominally the same capacity (and even of the same type and brand
bought at different times) tend not to be exactly the same size using a
partition a little smaller than the whole drive makes it certain that a
replacement drive will be big enough to use in the mirror when it arrives.
There's no need for that as ZFS can use same or bigger partition to
mirror existing one. If the second one would be smaller - do some math
and cut out some swap space.
--
Sphinx of black quartz, judge my vow.
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