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Date:      Sun, 14 Jun 2009 23:51:42 +0200
From:      Alson van der Meulen <alson+ml@alm.flutnet.org>
To:        freebsd-stable@freebsd.org
Subject:   Re: Does this disk/filesystem layout look sane to you?
Message-ID:  <20090614215142.GA32937@tafi.alm.flutnet.org>
In-Reply-To: <cf9b1ee00906140917j86b1e4ev4f8e0a1fb5f6b8@mail.gmail.com>
References:  <cf9b1ee00906140916n64a6c0cbr69332811bfa2aa62@mail.gmail.com> <cf9b1ee00906140917j86b1e4ev4f8e0a1fb5f6b8@mail.gmail.com>

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* Dan Naumov <dan.naumov@gmail.com> [2009-06-14 18:17]:
> I just wanted to have an extra pair (or a dozen) of eyes look this
> configuration over before I commit to it (tested it in VMWare just in
> case, it works, so I am considering doing this on real hardware soon).
> I drew a nice diagram: http://www.pastebin.ca/1460089

Looks fine to me. 

Note that your swap doesn't have any redundancy, so if you lose a disk,
the kernel will likely panic as soon as it hits any swap (the swap space
is striped across the disks), this is something you can easily test in a
VM. The kernel will only use four swap devices by default. I would put
the swap on gmirror. Swap performance is rarely critical (if you're
hitting swap often you should buy more RAM), and if you have 2TB disks,
a few extra gigabytes less is not an issue (I usually make swap slightly
larger than RAM for crash dumps, sometimes twice that if I plan to add
RAM later).

> Is there any actual downside to having a 5-way mirror vs a 2-way or a 3-way one?

Write performance is slightly slower than a single disk (you have to
wait for all five disks to finish), but these partitions are rarely
performance-critical. Depending on your workload, it may be an issue
for /var (databases, logs, mail), but you could always move that data to
a ZFS filesystem. It should be fine for a file server. Any other
solution would just add more complexity.

Alson



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