ZFS: root pool considerations, multiple pools on the same disk

[Peter Jeremy]

On 2011-Dec-19 12:46:22 +0000, Hugo Silva <hugo at barafranca.com> wrote:
>I've been thinking about whether it makes sense to separate the rpool
>from the data pool(s)..

I think it does.  I have 6 1TB disks with 8GB carved off the front of
each disk for root & swap.  I initially used a separate (gmirrored)
UFS root (including /usr/src and /usr/obj) because I didn't completely
trust ZFS.  I've since moved to a 3-way mirrored ZFS root, with the
"root" area of the remaining 3 disks basically spare (I use them for
upgrades).  The bulk of the disks form a 6-way RAIDZ2 data pool.

I still think having a separate root makes sense because it should
simplify recovery if everything goes pear-shaped.

>One idea would be creating a 4-way mirror on small partitions for the
>rpool (sturdier), and a zfs raid-10 on the remaining larger partition.

I'd recommend having two 2-way mirrored root pools that you update
alternately.  There are a couple of failure modes where it can be
difficult to difficult to get back to a known working state without
a second boot/root.

>I'm curious about the performance implications (if any) of having >1
>zpools on the same disks (considering that during normal usage, it'll be
>the data pool seeing 99.999% of the action) and whether anyone has
>thought the same and/or applied this concept in production.

I haven't done any performance comparisons but would expect this to
be similar to having multiple UFS filesystems on one disk.

-- 
Peter Jeremy
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