[mythtv-users] RAID using two drives per PATA channel ?

Fedor Pikus fpikus at gmail.com
Tue Aug 1 01:27:41 UTC 2006

On 7/31/06, Brad Templeton <brad+myth at templetons.com> wrote:
> On Mon, Jul 31, 2006 at 06:08:50PM -0700, Brad Templeton wrote:
> > On the other hand, high performance is desired for your regular linux
> > partitions.   They are of course much smaller.  You might consider
> > raid 1+0 on 4 drives for them, and raid-5 on 4 drives for the video
> > files.   (Software raid, typically for this ability.)
> Whoops, I should add that if your raid 1+0 is done with master/slaves
> it could take the hit there.   A Raid 0 (stripe) done to 2 drives, both
> masters, would be happy but that's not redundant.   A raid where you
> stripe over controllers and mirror over slaves would be slower on write
> that having 4 dedicated controllers, but presumably just as fast on read.
> As for one drive locking out the other one, if you fear that, then
> this is not for you, but you're not trying to build servers for ebay
> here, it's a tv recorder.  For me, I can handle if the system hangs
> as long as I can recover all my data after I attend to it.
> _______________________________________________

There are two levels of recovery to consider here. If you have one
drive per channel, you can usually just replace the failed drive and
everything works. Note that if you have to plug in PCI cards to get
more IDE ports, some of these cards can be taken down by a single
failed drive even if the drives are connected to separate interfaces.
If you want to make sure your data can be recovered, but you don't
mind working for it on a rare occasion that a disk fails, you can
always recover from a two-disk temporary failure by recreating the
RAID, as long as you have recorded the proper order of disks in mdadm
command. Also be sure that you know which drive corresponds to which
drive letter (not a problem for ATA on the motherboard, but if you
plug in PCI cards it can be uncertain): if you unplug the wrong drive
you now have a two-disk failure.

Fedor G Pikus (fpikus at gmail.com)

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