gmirror disks vs partitions

[Scott Long]

Andrew Pantyukhin wrote:
> On 1/17/07, Josef Karthauser <joe at 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.

The head movement that this causes makes it a poor performer.  It is
an option, but not a terribly popular one.

Scott