On Fri, 17 Feb 2012, Freddie Cash wrote:
On Fri, Feb 17, 2012 at 3:12 AM, Pete French <petefre...@ingresso.co.uk> wrote:
I wasn't aware you could do that. I was only aware that it was the
other way around. That (my) misconception seems to also be relayed
by others such as Miroslav who said:
Should this not be the recommended way of doing things even for MBR
disks ? I have a lot of machines booting from gmirror, but we always
do it by mirroring MBR partitions (or GPT ones). I cant see why you would
want to do it the other way round in fact. It doesnt gain you anything
does it ?
The problem with mirroring partitions is that you thrash the disk
during the rebuild after replacing a failed disk.
Potentially, yes.
And the more partitions you have, the worse it gets.
One big mirrored partition avoids it, but then there's only one
partition. (ad0p2a? Forget I mentioned that.)
If you mirror the device, then the rebuild process only has to rebuild
a single "thing".
If you mirror 4 partitions on a device, then there will be four
simultaneous, parallel rebuild processes running, thrashing the drive
heads on both devices, killing you I/O throughput and extending the
length of the rebuild.
Some queuing logic in the mirror rebuild could avoid that. I am
blissfully unaware of how complicated that might be._______________________________________________
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