Date: Tue, 16 May 2017 16:00:15 -0700 From: Aaron <drizzt321@gmail.com> To: freebsd-questions@freebsd.org Subject: Re: ZFS root on single SSD? Message-ID: <CAEsW2o9xDtD%2BK0=BsNhWgWn%2BJr1Os38Eu-6yJzO-uzAXrLfDBA@mail.gmail.com> In-Reply-To: <20170516222456.q3wuwlthgpoup7md@ozzmosis.com> References: <CAEsW2o88qA_YGxHC%2B5nWsi90yJfXKkCSV7tACstK6_hLNgu4HQ@mail.gmail.com> <20170516222456.q3wuwlthgpoup7md@ozzmosis.com>
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--Aaron On Tue, May 16, 2017 at 3:24 PM, andrew clarke <mail@ozzmosis.com> wrote: > On Mon 2017-05-15 22:45:19 UTC-0700, Aaron (drizzt321@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. > Ah, I guess I just assumed UFS had it, I hadn't actually checked. Thanks! > > > 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 > > https://forums.freenas.org/index.php?threads/single-drive-zfs.35515/ > > 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 > backups. > > 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. > > Regards > Andrew > I think most modern SSDs have pretty good checks because of how they use MLC/TLC NAND and how it fails. The biggest thing I can think of is a controller/board failure, rather than suddenly having massive number of blocks fail. However, it is a point that without copies=2 (or more) while bit-rot/corruption would be detectable, it wouldn't be possible to re-construct the bad blocks. Side note, copies=2 resiliency test ( http://jrs-s.net/2016/05/09/testing-copies-equals-n-resiliency/), rather interesting, although I probably won't be using it, at least not for an SSD. --Aaron
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