On Mon, 1 Nov 2004 15:22:17 +0100, Frank Gevaerts <[EMAIL PROTECTED]> wrote: > On Mon, Nov 01, 2004 at 09:28:32AM +0800, Paolo Alexis Falcone wrote: > > RAID 5 alleviates this by using parity information stored across the > > disks - now it takes more than 1 disk failure for RAID 5 to fail. > > How does this change anything ? If you have one failed disk, and one > disk containing unknown errors (the same case as your RAID1 example > above), replacing the failed disk will lead to errors on the new disk.
The use of parity information in separate blocks for reads and writes would just reduce the risk of that happening (prolonging the inevitable?) as data information and parity information are distributed across all disks in the array (RAID 1 won't contain parity information, and is just a copy - data and all) . The disadvantage, of course, with this setup, the controller design would be a lot more complicated and subsequently would make the array reconstruction more difficult unlike RAID 1 wherein it's guaranteed that you'd get a copy of the other half of the mirror. Whether that remaining half of the mirror already got checked for other errors that might've seeped in is another matter absent of RAID 1 though as RAID 1 doesn't have a provision for other information other than merely write data to the other disk as well. On an environment that's heavy on writes, RAID 5's overhead doesn't really justify the costs. You'd be better off with RAID 1 for that. -- Paolo Alexis Falcone [EMAIL PROTECTED] -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
