Date: Tue, 16 May 2017 06:34:38 -0400 From: "jim@ohlste.in" <jim@ohlste.in> To: Aaron <drizzt321@gmail.com> Cc: freebsd-questions@freebsd.org, Matthew Seaman <matthew@FreeBSD.org> Subject: Re: ZFS root on single SSD? Message-ID: <9997fd01-273c-b176-b9ed-e33e9e2d1b2f@ohlste.in> In-Reply-To: <99fa2537-9fb1-0ccf-d906-39db1c2e2685@FreeBSD.org> References: <CAEsW2o88qA_YGxHC%2B5nWsi90yJfXKkCSV7tACstK6_hLNgu4HQ@mail.gmail.com> <99fa2537-9fb1-0ccf-d906-39db1c2e2685@FreeBSD.org>
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Hello, On 05/16/2017 03:39 AM, Matthew Seaman wrote: > 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. > > Cheers, > > Matthew > > [*] With only one drive and one copy of each file, ZFS cannot provide > resilience against data errors, but it will prevent it going unnoticed. > I'd add only that while a mirrored zpool offers some data protection, it is *not* an effective "backup" solution for important data. Drive failure during resilver after a drive replacement does occur. If there's important data on the drive, backing it up to a different medium is still essential, whether it's a mirrored pool or a single drive pool. [Leaned once the hard way]™ -- Jim Ohlstein
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