RE: Reverse of XOR.

How interesting.  I had thought that the RAID-5 protection method was based
upon parity instead of XOR.

-----Original Message-----
From: Leif Svalgaard [mailto:leif@leif.org]
Sent: Tuesday, August 27, 2002 8:19 AM
To: mi400@midrange.com
Subject: Re: [MI400] Reverse of XOR.


From: Walden H. Leverich <WaldenL@TechSoftInc.com>
> >From: James H. H. Lampert [mailto:jamesl@hb.quik.com]
> >This, by the way, is why XOR operations are often used for graphics
> And more relevant to the iSeries, XOR is the basis for RAID-5 disk
> subsystems. Given three drives:
>
> Bit Drive1 Drive2 Drive3
> 1 1 1 0
> 2 1 0 1
> 3 0 0 1
> 4 0 1 1
>
> Etc. Remove (crash) any one of those drives and you can recover the data
on
> it by XOR-ing the data on the other two drives.
>

for this to work the disks have to written correctly.
You example is not too good. Remove Drive3 and
try to recover it (fails for bit 3)

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