ZFS root on single SSD?

andrew clarke mail at ozzmosis.com
Tue May 16 22:25:12 UTC 2017

On Mon 2017-05-15 22:45:19 UTC-0700, Aaron (drizzt321 at gmail.com) wrote:

> So, I've been running ZFS root mirror across 2 spinning disks, and I'm
> upgrading my home server/nas and planning on running root on a spare SSD.
> However, I'm unsure if it'd be better to run UFS as a single drive root
> instead of ZFS, although I do love all of the ZFS features (snapshots, COW,
> scrubbing, etc) and would still like to keep that for my root drive, even
> if I'm not mirroring at all. I do notice that FreeBSD has TRIM support for
> ZFS (see http://open-zfs.org/wiki/Features#TRIM_Support).

ICYMI, FreeBSD also has TRIM support for UFS. See the -t flag for the
newfs command.

> So is there a good reason NOT to run ZFS root on a single drive SSD?

A good question that I've often wondered about.

The first reply at


hints at metadata corruption on a pool located entirely on a single
magnetic drive possibly leading to failure of the entire pool, and
given the lack of easy to use repair tools for ZFS, would require a
rebuild. I think in reality this would be quite rare though, and
hopefully wouldn't be a huge issue anyway provided you keep regular

Using an SSD might change things a little should the drive begin to
fail, but I get the impression modern SSDs tend to fail a bit more
gracefully than the old ones. I've no experience here and am
interested in any anecdata.

Keep in mind you also have other options, such as splitting the drive
into separate UFS and ZFS partitions, or creating a ZFS pool from a
file on UFS. The latter probably has performance drawbacks, but they
might be negated by the performance of the SSD.


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