On Fri, Jun 24, 2016 at 3:52 AM, Andrei Borzenkov <arvidj...@gmail.com> wrote: > On Fri, Jun 24, 2016 at 11:50 AM, Hugo Mills <h...@carfax.org.uk> wrote: >eta)data and RAID56 parity is not data. >> >> Checksums are not parity, correct. However, every data block >> (including, I think, the parity) is checksummed and put into the csum >> tree. This allows the FS to determine where damage has occurred, >> rather thansimply detecting that it has occurred (which would be the >> case if the parity doesn't match the data, or if the two copies of a >> RAID-1 array don't match). >> > > Yes, that is what I wrote below. But that means that RAID5 with one > degraded disk won't be able to reconstruct data on this degraded disk > because reconstructed extent content won't match checksum. Which kinda > makes RAID5 pointless.
I don't understand this. Whether the failed disk means a stripe is missing a data strip or parity strip, if any other strip is damaged of course the reconstruction isn't going to match checksum. This does not make raid5 pointless. -- Chris Murphy -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
