Kyle McDonald writes: > Ross wrote: > > Just re-read that and it's badly phrased. What I meant to say is that a > > raid-z / raid-5 array based on 500GB drives seems to have around a 1 in 10 > > chance of loosing some data during a full rebuild. > > > > > > > Actually, I think it's been explained already why this is actually one > area where RAID-Z will really start to show some of the was it's > different than it's RAID-5 ancestors. For one, A RAID-5 controller has > no idea of the filesystem, and there for has to rebuild every bit on the > disk, whether it's used or not, and if it cant' it will declare the > whole array unusable. RAID-Z on the other hand since it is integrated > with the filesystem, only needs to rebuild the *used* data, and won't > care if unused parts of the disks can't be rebuilt. > > Second, a factor that the author of that article leaves out is that > decent RAID-5, and RAID-Z can do 'scrubs' of the data at regular > intervals, and this will many times catch and deal with these read > problems well before they have a chance to take all your data with them. > The types of errors the author writes about many times are caused by how > accurately the block was written and not a defect of the media, so many > times they can be fixed by just rewriting the data to the same block. On > ZFS this will almost never happen, because of COW it will always choose > a new block to write to. I don't think many (if any) RAID-5 > implementaions can change the location of data on a drive. >
Moreover, ZFS stores redundant copies of metadata so even if a full raid-z stripe goes south, we can still rebuild most of pool data. It seems that at worst, such double failures would lead to a handful of un-recovered files. -r > -Kyle > > > This message posted from opensolaris.org > > _______________________________________________ > > zfs-discuss mailing list > > zfs-discuss@opensolaris.org > > http://mail.opensolaris.org/mailman/listinfo/zfs-discuss > > > > _______________________________________________ > zfs-discuss mailing list > zfs-discuss@opensolaris.org > http://mail.opensolaris.org/mailman/listinfo/zfs-discuss _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
