On Wed, 30 Jul 2014 15:05:29 +0200 Gionatan Danti <g.danti@xxxxxxxxxx> wrote: > On 30/07/2014 13:13, Mikael Abrahamsson wrote: > > > > There has been much discussion about the URE figures. Some people > > interpret it one way, others another way. There is nobody here that > > knows for sure. Ask your HDD vendor, if they answer, do share here! > > > - Ouch! - > I was hoping that HDD vendors were somewhat more open about their URE > calculations... It's time for some lab test, I think! > > > > When MD encounters an URE, it should calculate that block from parity > > information and write it. I have personally had problems with this not > > happening, seems it might be that if the URE doesn't happen repeatedly, > > MD might not re-write. All parity raid levels should behave the same, so > > this should work identically for RAID1, RAID10, RAID5 and RAID6. > > > What about _degraded_ array state? In other words, if a degraded RAID5 > experiences a URE during rebuild, what happens? I read that most > hardware based RAID card both stop rebuilding _and_ kill the entire > array. From my understanding, mdadm should stop rebuilding but the array > can the restarted, mounted and backupped. Right? > > Regards. > Yes, you can usually get your data back with mdadm. With latest code, a URE during recovery will cause a bad-block to be recorded on the recovered device, and recovery will continue. You end up with a working array that has a few unreadable blocks on it. NeilBrown
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