On Tue, 12 Jun 2012 18:34:52 +0200 Edgar Fuß <[email protected]> wrote:
> > So a parity rebuild does so by reading all the data and the > > exiting parity, computing the new parity, and then comparing the > > existing parity with the new parity. If they match, it's on to the > > next stripe. If they differ, the new parity is written out. > Oops. > What's the point of not simply writing out the computed parity? Writes are typically slower, so not having to do them means the rebuild goes faster... > > What we don't know here is what the state of the array was when you > > started the rebuild. That is, was the parity 'mostly correct' > > beforehand? (i.e. saving having to do a lot of the writes). > I don't know either. If the discs contained a clean RAID set with a > different SPSU, was the parity correct? For a basic RAID 5 set yes, it would be. The exception might be at the very end of the RAID set where a smaller stripe size might allow you to use a bit more of each component. Later... Greg Oster
