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From: "Andrew Pantyukhin" <infofarmer@FreeBSD.org>
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Subject: Re: gmirror disks vs partitions
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On 1/17/07, Josef Karthauser <joe@freebsd.org> wrote:
> A poll for opinions if I may?
>
> I've got a few gmirrors running on various machines, all of which
> pair up two drives at the physical level (i.e. mirror /dev/ad0s1
> with /dev/ad1s1).  Of course there are other ways of doing it to,
> like mirroring at the partition level, ie pairing /dev/ad0s1a with
> /dev/ad1s1a, /dev/ad0s1e with /dev/ad0s1e, etc.
>
> Apart from potentially avoiding a whole disk from being copied
> during a resync after a crash, are there any other advantages to
> using partition level mirroring instead of drive level mirroring?

I can imagine people using partition-level raid to
implement a popular configuration:

You divide a couple of identical drives proportionally
in two partitions each, place a couple of the first
partitions into gmirror and a couple of the second
ones into gstripe. This way you get both reliable and
fast storage with just two drives. Some strings are
attached.