SATA PT2

[Phil Thayer]

If you do that you need to make sure that the controller will support
RAID 6 or RAID ADG.  This is simply a RAID 5 with an additional parity
disk implemented.  This reduces the risk of failure of the entire RAID
if a single disk fails.  The RAID will simply function as if it were a
RAID 5 until the failed disk is physically replaced and the RAID 6 or
RAID ADG is rebuilt.

As an alternative, if you have a controller that does not have RAID 6 or
RAID ADG, then you can use RAID 5 with a spare disk set aside for use as
a spareset in case of a failure.  This does not eliminate the risk in
case of a single disk failure but it reduces it to the time required to
rebuild the RAID using the spareset as opposed to the time it takes to
physically replace a drive in a degraded RAID 5. If you suffer a second
disk drive failure during the time that the RAID 5 is rebuilding after
the first disk drive failure, then you will loose your entire RAID.

The ultimate high availability configuration would be RAID 60+.  This
would be two RAID 6 with their own sparesets assigned, mirrored to each
other.  However, be prepared to loose a larger percentage of your raw
disk drive space.  You will loose the equivalent of:

Two disk drives for each RAID 6 used
Two disk drives for each RAID 6 for redundant sparesets
One raid 6 with the mirroring

I really don't expect that you would build something like that for a
home server but I figured I would throw all that out there just in case
you had more money that you know what to do with and want to make sure
the data on your server is safe from failure.

Phil

> -----Original Message-----
> From: kclug-bounces at kclug.org 
> [mailto:kclug-bounces at kclug.org] On Behalf Of Luke-Jr
> Sent: Tuesday, June 05, 2007 9:20 AM
> To: kclug at kclug.org
> Subject: Re: SATA PT2
> 
> On Tuesday 05 June 2007 09:11, Phil Thayer wrote:
> > Not to mention that with the recent SATA drive sizes to get 
> 1TB of SATA
> > would only take 2 drive.  However, if you want to use a 
> multi-channel
> > SATA controller with raid you will want to use smaller 
> drives (like 4 x
> > 300 or 8 X 250) so you don't loose too much capacity to parity.
> 
> With 8 drives, I'd probably want to make 2 parity for a 
> server... As unlikely 
> as it is for 2 drives to fail at once, that chance does 
> increase with # of 
> drives.
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