On Dec 6, 2007 2:58 PM, Aaron Kulkis <[EMAIL PROTECTED]> wrote: > > Chris Worley wrote: > > On Dec 6, 2007 10:26 AM, Aaron Kulkis <[EMAIL PROTECTED]> wrote: > >> Chris Worley wrote: > >>> On Dec 5, 2007 5:12 PM, Aaron Kulkis <[EMAIL PROTECTED]> wrote: <snip> > > To do a write to block #X on Drive A, Block #X on the parity > drive must be updated, which means that Block #X on drives > B, C, ... must also be read, and all of them XOR'ed together > before you can write the parity block on the parity device. > I think you saying that to update a sector on a 10-disk raid5 you would have to read from most of the drives to recreate the parity. Fortunately XOR is a reversible process.
ie A ^ B ^ B = A (Where A is the parity without the data on sector B) So just 2 reads and 2 writes are needed. (See my earlier post). Greg -- Greg Freemyer Litigation Triage Solutions Specialist http://www.linkedin.com/in/gregfreemyer First 99 Days Litigation White Paper - http://www.norcrossgroup.com/forms/whitepapers/99%20Days%20whitepaper.pdf The Norcross Group The Intersection of Evidence & Technology http://www.norcrossgroup.com -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
