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

[Steven Adeff]

On 8/2/06, chris at cpr.homelinux.net <chris at cpr.homelinux.net> wrote:
> On Tue, Aug 01, 2006 at 05:21:33PM -0400, Steven Adeff wrote:
> > the drive bay has built in cooling via 2 huge fans, so I'll limit
> > myself to 6 drives).
>
> Don't trust the cooling fans.  When I built my RAID-5 system I bought a
> special 3-drive bay with a large filtered fan.  After installing the
> drives as per the directions, one of them started failing within a few
> days.  The top drive was getting soaked from below, and was
> uncomfortably hot to touch.  I pulled it from the bay and mounted it in
> an un-cooled internal bay and everything was fine.  From now on I'm
> going to buy single-drive pull-out bays with individual cooling.

except!... the drives are mounted like this:

| | | | | |

with the top being where you plug the cables in, and the fans blowing
"into the page" (ahh, vector math on a two dimensional surface...).
with the fans pulling in air through a filter from the front of the
case. They're big fans, one per 3 drives, and sadly rather noisy, but
they do push a lot of air and are in a "closet" so the noise isn't an
issue. In the end, not really worried about it...

> > I figure, since I have the space and the ability
> > in one form or another to have a 6 drive RAID 10 array for recordings,
> > whats the best way to go about it from where I am....
>
> You know you would have the same capacity if you used 4 drives in a
> RAID-5 array, right?  That's 33% less money/electricity/heat, and
> you might be able to avoid putting two drives on one IDE channel so
> performance wouldn't suck.  Software RAID-5 is not the performance
> pig some people make it out to be *IF* you have each drive on its
> own controller.

I had it RAID5 when I only had three drives, it wasn't enough for my 3
HD tuners, 1 SD tuner and HD capable frontends. Now with my 4 drive
RAID 10 it can keep up as long as its not commflagging or transcoding.
I'm not really going for size (its a nice included), but the overall
speed, considering I most likely will be adding an additional SD tuner
and one more HD capable frontend. I'm also hoping to be able to handle
all this while also performing commflagging and transcoding.

So my concern with RAID5 is the slow write speeds, which was my issue
before with RAID5, I just couldn't get it to keep up with everything.

I'm also trying to figure out a way to speed up the DB read/write,
thus my RAM drive question in another email.

-- 
Steve
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