RAM and zfs and multiple disks

[John]

On Thu, Oct 10, 2013 at 10:16:47AM -0700, Freddie Cash wrote:

> 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).

Thanks for the input. Can you share what your spec and tunables were?
Although I have it deployed on a freebsd host machine, (where with lots
of HD and RAM It Just Works), I've never deployed it on a desktop. That
being said, the host needs tuning, I'd like to bring it up to
10-current though before doing that.

The desktop machine currently runs 9.2 and has three x1TB disks. I've read in
the literature that it's best to have them all the same size or space is lost.
I have also read that for raidZ you really need more than 2 and less than 10
so maybe make the three I already have as one raidz array and get 4x 4TB and
make another array. All will be SATA 2 or 3. What do you think? Basically
the whole reason for me having ZFS on the desktop is guarding against 
bitrot and failure of a single drive in an array. I'm really happy that
you've been able to move the same data across architectures - that's a relief
as my desktop is getting on a bit.

thanks,
-- 
John