On Thu, Oct 11, 2012 at 2:47 PM, andy thomas <a...@time-domain.co.uk> wrote:
> According to a Sun document called something like 'ZFS best practice' I read
> some time ago, best practice was to use the entire disk for ZFS and not to
> partition or slice it in any way. Does this advice hold good for FreeBSD as
> well?
Solaris disabled the disk cache if the disk was partitioned, thus the
recommendation to always use the entire disk with ZFS.
FreeBSD's GEOM architecture allows the disk cache to be enabled
whether you use the full disk or partition it.
Personally, I find it nicer to use GPT partitions on the disk. That
way, you can start the partition at 1 MB ("gpart add -b 2048" on 512B
disks, or "gpart add -b 512" on 4K disks), leave a little wiggle-room
at the end of the disk, and use GPT labels to identify the disk (using
gpt/label-name for the device when adding to the pool).
> Another point about the Sun ZFS paper - it mentioned optimum performance
> would be obtained with RAIDz pools if the number of disks was between 3 and
> 9. So I've always limited my pools to a maximum of 9 active disks plus
> spares but the other day someone here was talking of seeing hundreds of
> disks in a single pool! So what is the current advice for ZFS in Solaris and
> FreeBSD?
You can have multiple disks in a vdev. And you can multiple vdevs in
a pool. Thus, you can have hundred of disks in a pool. :) Just
split the disks up into multiple vdevs, where each vdev is under 9
disks each. :) For example, we have 25 disks in the following pool,
but only 6 disks in each vdev (plus log/cache):
[root@alphadrive ~]# zpool list -v
NAME SIZE ALLOC FREE CAP DEDUP HEALTH ALTROOT
storage 24.5T 20.7T 3.76T 84% 3.88x DEGRADED -
raidz2 8.12T 6.78T 1.34T -
gpt/disk-a1 - - - -
gpt/disk-a2 - - - -
gpt/disk-a3 - - - -
gpt/disk-a4 - - - -
gpt/disk-a5 - - - -
gpt/disk-a6 - - - -
raidz2 5.44T 4.57T 888G -
gpt/disk-b1 - - - -
gpt/disk-b2 - - - -
gpt/disk-b3 - - - -
gpt/disk-b4 - - - -
gpt/disk-b5 - - - -
gpt/disk-b6 - - - -
raidz2 5.44T 4.60T 863G -
gpt/disk-c1 - - - -
replacing - - - 932G
6255083481182904200 - - - -
gpt/disk-c2 - - - -
gpt/disk-c3 - - - -
gpt/disk-c4 - - - -
gpt/disk-c5 - - - -
gpt/disk-c6 - - - -
raidz2 5.45T 4.75T 720G -
gpt/disk-d1 - - - -
gpt/disk-d2 - - - -
gpt/disk-d3 - - - -
gpt/disk-d4 - - - -
gpt/disk-d5 - - - -
gpt/disk-d6 - - - -
gpt/log 1.98G 460K 1.98G -
cache - - - - - -
gpt/cache1 32.0G 32.0G 8M -
--
Freddie Cash
fjwc...@gmail.com
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