RAM and zfs and multiple disks

[Freddie Cash]

On Thu, Oct 10, 2013 at 10:07 AM, John <freebsd-lists at potato.growveg.org>wrote:

> I'd like to have zfs on my freebsd desktop. However,
> this motherboard can take 8GB RAM, max.
>
> I'd like to get 2 x4Tb drives. Realistically, do I
> need another motherboard? The primary reason to have ZFS
> is to guard against bitrot
> ​.
>

I ran ZFS on a 32-bit install of FreeBSD using a 3.0 GHz P4 with only 2 GB
of RAM for several years.

Started with 4x 160 GB drives in a raidz1 vdev and FreeBSD 8.x with / on
UFS on a USB stick.

Migrated to 2x 500 GB drives in a mirror vdev and FreeBSD 9.0, still with /
on UFS on a USB stick.

Migrated to 4x 1.0 TB drives in 2 mirror vdevs and PC-BSD 9.1, with
ZFS-on-root (no USB sticks).  At this point, I switched to a 64-bit install
running on an Athlon-II CPU with 4 GB of RAM.

Finally, migrated to "rolling-release" of PC-BSD (which shows as TruOS in
uname) based on FreeBSD 9-STABLE (post 9.1) running on a Phenom-II X4 with
8 GB of RAM.

Beauty of ZFS snapshots send/recv and boot environments is that I didn't
lose any data during any of the migrations, and was able to reconfigure the
pool a couple of times.  And switch from 32-bit to 64-bit FreeBSD (only
saved /home for that one).

IOW, you don't need a tonne of RAM to run ZFS.  You just need to spend some
time tweaking ZFS-related tunables in /boot/loader.conf to guard against
lockups due to lack of kmem (really only an issue on a 32-bit system due to
kmem fragmentation).

And, definitely do NOT enable dedupe on a system with multiple TB of
storage unless you have 16+ GB of RAM!  Compression is fine (running with
lz4 on my home system now; originally was lzjb+gzip).

-- 
Freddie Cash
fjwcash at gmail.com