RAID questions (was Re: [TriLUG] Re: Dieing hard drive?)

[Ben Pitzer]

Tanner,

I agree heartily with Aaron this time.  RAID 5 is not what you'd want
outside of an external array, or in a box with half a dozen drives.  For
your purposes, RAID 1+0 is probably the best.  I use it on my Sun Blade at
work, and I've decided that my next box for home will have 1+0.  Basically,
you'd need two drives of identical size (although I'm not sure the identical
part is requisite, but it does ensure that you won't have compromised data
if the data being stored is larger than the size of the smaller drive).
RAID 1+0 is basically striped mirrors, providing better fault tolerance than
RAID 5 or RAID 0+1, but somewhat slower i/o rates, I believe.  One provides
better read performance, and one better write performance, IIRC.  If I'm not
mistaken, somebody did a write-up of RAID levels here a while back that was
pretty good.  Anybody have it for a repost?

Two things come to mind here, that are obstacles for RAID configurations.
First, you'll need to replace a failed drive with a new drive of the same
size and geometry, I believe.  That might get expensive, and unless you buy
a number of drives up front, you might have trouble finding a new drive with
the size and geometry you need.

Second, while you are buying two 160GB drives and basically have 320GB of
disk space, for example, you'll only get 160GB of total space after building
the RAID array.  Thus, you've just doubled the cost of your storage space,
which means you need to determine the cost/benefit ratio for your situation
before you go in.

Since it never fails that someone does it, c'mon, hit me with all of the
wrong information in my email.  Please.

Regards,
Ben Pitzer

---------------------------------------------

"Those that can give up essential liberty to obtain a little temporary
safety deserve neither liberty nor safety."
 --Ben Franklin--




> -----Original Message-----
> From: trilug-bounces at trilug.org [mailto:trilug-bounces at trilug.org]On
> Behalf Of Aaron S. Joyner
> Sent: Tuesday, November 30, 2004 1:41 PM
> To: Triangle Linux Users Group discussion list
> Subject: Re: RAID questions (was Re: [TriLUG] Re: Dieing hard drive?)
>
>
> Tanner Lovelace wrote:
>
> >While we're talking about RAID what version of RAID would people
> >suggest?
> >
> IMHYAO, Raid 5 is only a good choice if you are using a large number of
> drives, and can incorporate a hot spare or two - or if you really can't
> afford to sacrifice 50% of the capacity of the purchased drives.
>
> >Also, should I consider getting a "$20 IDE RAID controller" or just
> >use software RAID?
> >
> >
> I'd generally suggest the controller.  The advantage being that it gives
> you another set of IDE channels to attach those drives to (as you may
> need them since they is not going to be your only disks).  It also
> pretty-much ensures that you're going to have hot-swappable channels,
> which is a nice feature in a RAID setup, given that one of the main
> purposes of RAID is to keep things up and running should a disk die.
> Another consideration in the RAID 5 vs mirroring debate is that most
> cheap RAID cards can't do RAID 5, and it is a larger software hit to do
> the checksumming and other processing on the host system.
>
> Aaron S. Joyner
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