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

[John Andersen]

On 7/31/06, Steven Adeff <adeffs.mythtv at gmail.com> wrote:

> > 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.
>
> I'll just wait till I can afford 4x new SATA drives then.
>
> thanks for the info all!

However:  IDE raid arrays using software raid ave been wildly
successfull, riveling (and often beating) the preformance of dedicated
hardware raid cards.

I have a number of servers where I was using the inexpensive dedicated
hardware raid cards, and found that by disabling the raid support on
the card and using its two independent ide channels that i actually
got BETTER performance than using the onboard raid.  (I did this
because software raid is more flexible, allowing me to mix dissimilar
drive types.  I was supprised at the result initially.  Its counter
intuitive.

Inexpensive IDE controllers allow you to build arrays with a single drive on
each cable, because they support (usually) two or four distinct
channels per card, so even when you DON'T want to use their raid
capability, the cards are cheap and usefull.

If you MUST use two disks per channel just make sure they are not in
the same raid array for performance reasons.  That way, your only real
risk is the entire channel being taken down by a single disk, which
(contrary to the scary stories posted here) seldom happens in real
life.  Disks usually fail mechanically, not electrically, and the
onboard logic times out waiting for data
and the bus becomes available again, and usually well within the time
your cashing can handle.

-- 
----------JSA---------