ZFS root on single SSD?

Matthew Seaman matthew at FreeBSD.org
Tue May 16 07:39:51 UTC 2017

On 16/05/2017 06:45, Aaron 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).
> So is there a good reason NOT to run ZFS root on a single drive SSD?

No.  Running ZFS on a single device works fine, although you obviously
don't benefit from all the really nice resilience features.

The choice between UFS2 and ZFS basically comes down to three points:

   * performance -- for certain IO patterns, UFS can out-perform ZFS
quite markedly.  Particularly the sort of small, randomly distributed
IOs you get with a RDBMS.  Of course, for database use, the additional
data security you get from ZFS makes it desirable despite this.

   * system resources -- ZFS is memory hungry.  This is not a problem on
most contemporary machines, which tend to have sufficient RAM, but older
machines, VMs or appliances may struggle.

   * data security -- the integrated checksumming in ZFS provides
assurance that the data you're reading now is the same as what you wrote
previously.  Now, this is almost always the case with UFS2 (would be
entirely useless if not), but there is no actual guarantee of it, and
silent data corruption is possible[*].  If you're handling data which is
really important or in particularly large volumes or where your hardware
may prove deficient, then ZFS is indicated.



[*] With only one drive and one copy of each file, ZFS cannot provide
resilience against data errors, but it will prevent it going unnoticed.

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