SATA PT2

[Phil Thayer]

I didn't think RAID 5 or RAID 6 kept all parity data on any one
particular disk.  I thought it was spread across all the disks. In the
case of RAID 6 I thought that the parity was stored on different disks
each time but never both on the same disk.

In any case, I think you both may be right.  They are using a different
parity algorithm for the second parity to be able to recover from a
multiple disk failure which would cause the loss of multiple bits of the
data.  My bad on that one.

> -----Original Message-----
> From: kclug-bounces at kclug.org 
> [mailto:kclug-bounces at kclug.org] On Behalf Of Luke -Jr
> Sent: Wednesday, June 06, 2007 12:39 PM
> To: kclug at kclug.org
> Subject: Re: SATA PT2
> 
> On Wednesday 06 June 2007 09:47, Phil Thayer wrote:
> > As for figuring out the second parity calculation on RAID 
> 6, what the
> > manufacturers are realizing is that they don't necessarily 
> have to have
> > a different parity algorithm to calculate the second parity.  Simply
> > putting the same XOR parity data on two separate disks will 
> provide the
> > same RAID 6 functionality as having a second parity calculation with
> > lower overhead on controllers.  The old KISS methodology is 
> coming back
> > into play.  I think you will see more and more of the manufacturers
> > going this route.
> 
> That only works if one of the dead disks is a parity disk...
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