On Wed, Apr 26, 2006 at 03:22:38PM -0400, Jon Lewis wrote: > On Wed, 26 Apr 2006, Jansen, Frank wrote: > > >It is not possible to flip a bit to change a set of disks from RAID 1 to > >RAID 5, as the physical layout is different. > > As Tuomas pointed out though, a 2 disk RAID5 is kind of a special case > where all you have is data and parity which is actually also just data. No, the other way around: RAID1 is a special case of RAID5. The parity of RAID5 with n disks is contructed like[1]: parity = disk1 XOR disk2 XOR ... XOR disk n-1 With n = 2, this reduces to: parity = disk1 XOR nothing = disk1 Which is just mirroring, which we usually call "RAID1". > Seems kind of like a RAID1 with extra overhead. I don't think I've ever > heard of a RAID5 implementation willing to handle <3 drives though. Our own RAID recovery tools can handle that just fine. Erik [1] Yes, there's also an algorithm to select which disk is used for parity for what block, but that doesn't change the way *how* parity is calculated. -- +-- Erik Mouw -- www.harddisk-recovery.com -- +31 70 370 12 90 -- | Lab address: Delftechpark 26, 2628 XH, Delft, The Netherlands - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
