On Fri, Jan 2, 2009 at 10:47 AM, Mika Borner <opensola...@bluewin.ch> wrote:
> Ulrich Graef wrote: > > You need not to wade through your paper... > > ECC theory tells, that you need a minimum distance of 3 > > to correct one error in a codeword, ergo neither RAID-5 or RAID-6 > > are enough: you need RAID-2 (which nobody uses today). > > > > Raid-Controllers today take advantage of the fact that they know, > > which disk is returning the bad block, because this disk returns > > a read error. > > > > ZFS is even able to correct, when an error in the data exist, > > but no disk is reporting a read error, > > because ZFS ensures the integrity from root-block to the data blocks > > with a long checksum accompanying the block pointers. > > > > > > The Netapp paper mentioned by JZ > (http://pages.cs.wisc.edu/~krioukov/ParityLostAndParityRegained-FAST08.ppt<http://pages.cs.wisc.edu/%7Ekrioukov/ParityLostAndParityRegained-FAST08.ppt> > ) > talks about write verify. > > Would this feature make sense in a ZFS environment? I'm not sure if > there is any advantage. It seems quite unlikely, when data is written in > a redundant way to two different disks, that both disks lose or > misdirect the same writes. > > Maybe ZFS could have an option to enable instant readback of written > blocks, if one wants to be absolutely sure, data is written correctly to > disk. > Seems to me it would make a LOT of sense in a WORM type system. --Tim
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