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

[Jens Axboe]

On Mon, Jul 31 2006, Alexander Fisher wrote:
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> Steven Adeff wrote:
> > anyone have any insight in to whether when neglecting possible card or
> > cable failure, would using two drives on a single PATA channel for a
> > RAID 10 array to add two more drives lead to an overall increase in
> > the array speed, or would the speed loss be too great for the extra
> > drives to help any?
> 
> According to the linux RAID HOWTO...
> http://www.tldp.org/HOWTO/Software-RAID-HOWTO-4.html#ss4.1
> 'It is very important, that you only use one IDE disk per IDE bus. Not
> only would two disks ruin the performance, but the failure of a disk
> often guarantees the failure of the bus, and therefore the failure of
> all disks on that bus.'
> 
> Then again, the HOWTO is somewhat out of date.  Perhaps dieing disks
> killing the bus is just folklore?

Nope, that one still holds true. If the broken drive locks up the
bus, the other drive will be inaccessible as well.

Old parallel IDE has no concept of bus release, like SCSI. Access to the
bus is thus always serialized between the two drives, so you will see a
performance loss as well.

-- 
Jens Axboe