--- On Wed, 9/23/09, Robin Hill <robin@xxxxxxxxxxxxxxx> wrote:
> Obviously, but in the case of a RAID1 mirror, then this is
> immaterial
> (as either side of the mirror is identical), and in the
> RAID10 case it
> is controlled by the position of the drives in the array
> (which is
> controlled by the order they're given in the create
> statement).
>
> > When I set up my NAS it's likely those remote drives
> will be sdc and
> > sdd (HTPC drives would be sda and sdb), so the RAID10
> create order
> > wouldn't help.
> >
> Of course the create order helps - it's the _only_ way to
> control what
> chunks of the data go on which drive. If your HTPC
> ends up with local
> drives sda and sdb, and remote drives sdc and sdd, then
> do:
>
> mdadm -C /dev/md0 -l 10 -p n2 -n 4 /dev/sda
> /dev/sdc /dev/sdb /dev/sdd
>
> Then you'll end up with a RAID10 with all data held on both
> the sda/sdb
> and sdc/sdd pairs (so either pair can drop out of the array
> without
> losing any data). The data layout will be:
>
> sda sdb sdc sdd
>
> A1 A2 A1 A2
>
> A3 A4 A3 A4
> ...
>
> The equivalent happens for f2 or o2 arrays - though they're
> not strictly
> mirrored in those cases (they contain the same data but
> with a differing
> layout).
>
> As I say though, this setup will still result in poor
> performance as you
> have the database and recordings on the same drives.
> And to make them
> bootable you'd want to partition the drives first and
> create a separate
> 4-way RAID1 mirror for /boot.
YIKES, I'd better read this when I'm -not- drunk...
I take away that my main performance problem is in not separating by drive, the Myth database from the affected video. Given these listserv transactions, I guess I have to resort to a 2.5" drive with the root filesystem and the Myth database, and the space-divided array for video storage. I guess I can't RAID10 the root drive with the garage, as it might not be bootable, and you probably can't boot to a NAS drive anyway. But this doesn't stop me from backing up the root drive onto the array.
It seems that I -can- control the role of the drives using your command above. This is good news.
I will reexamine this tomorrow...
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