Date: Wed, 23 Dec 2015 17:53:41 +0000 From: Bob Bishop <rb@gid.co.uk> To: andrew clarke <mail@ozzmosis.com> Cc: Stephen Hocking <stephen.hocking@gmail.com>, hackers@freebsd.org Subject: Re: The minimum amount of memory needed to use ZFS. Message-ID: <26557C02-C591-4232-BBD0-988B0EB89575@gid.co.uk> In-Reply-To: <20151223121445.GA85016@ozzmosis.com> References: <CA%2BxzKjDQ_vUfgz4LvvcBE950=-ww7ukCbFmZz1vnzhGrNCucbQ@mail.gmail.com> <20151223121445.GA85016@ozzmosis.com>
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Hi, > On 23 Dec 2015, at 12:14, andrew clarke <mail@ozzmosis.com> wrote: >=20 > On Wed 2015-12-23 21:43:37 UTC+1100, Stephen Hocking = (stephen.hocking@gmail.com) wrote: >=20 >> Inspired by this article: >> = http://arstechnica.com/information-technology/2015/12/rsync-net-zfs-replic= ation-to-the-cloud-is-finally-here-and-its-fast/ >>=20 >> I am wondering about changing my offsite back strategy, which = currently is >> made up of a Raspberry Pi with an external 3TB drive sitting at my >> brother's house, with periodic manual rsyncs. I'd like to change that = to >> doing zfs replications. >>=20 >> I want to use some of my ARM based hardware as the target for the ZFS >> replication, owing to its low power usage. I have a few Cubiboxes = floating >> around with around 2G of RAM, and a RPI2 or a Banana Pi with 1G. It'd = have >> a UFS root on the SD card, and ZFS on the external drive. >>=20 >> Any ideas? >=20 > I'm curious about this too. >=20 > Currently I run a root-on-ZFS FreeBSD 10.2 amd64 system with 2 GB RAM > that I use for offline backups. The ZFS pool consists of 2 x 1 TB > drives in a mirror setup. I've never had FreeBSD run out of memory on > that machine. >=20 > I suggest you avoid using the deduplication feature of ZFS which from > what I understands likes to chew through memory. >=20 > I don't use ZFS snapshots on that machine, so can't speak about their > memory usage. Perhaps it's fairly insignificant, though. >=20 > An alternative might be to use something like rsnapshot, still on ZFS. >=20 > You might get a bigger audience if you ask on the freebsd-questions > list. >=20 > Regards > Andrew FWIW we have a backup box currently running 9.2 amd64 with 4GB RAM and a = ZFS mirror. We use rsync to transfer the data daily, and ZFS snapshots = to maintain a Time Machine-like structure (currently something over 150 = snapshots in play). We did have some instances of apparent memory = exhaustion until we limited vfs.zfs.arc_max to 2GB; that doesn=E2=80=99t = seem to have affected performance. Deduplication seems like a very bad idea unless you have both a lot of = duplicated data and a serious shortage of disk. It needs a lot of RAM, = increasing over time. Depending on the hardware and the use case, = compression (which effectively only costs CPU) might be a better option. -- Bob Bishop rb@gid.co.uk
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