On Oct 1, 2010, at 16:20, Douglas E. Engert wrote: > On 10/1/2010 4:35 AM, Harald Barth wrote: >> >> Another way to tackle the data corruption issue in the AFS case would >> be to add checksum functionality to the fileserver backend. In >> contrast to NFS, we have the advantage that noone reads the data >> directly from the file system but always through the client. > > ZFS stores the checksum of a block, not in the block, but in a higher level > block. This can then detect if a block failed to be written when its read > back. > Other file systems could not detect this, as they would read old data, > with an old checksum.
We've also seen disks randomly reading and returning a different sector than the one requested. > Keep this in mind if checksums are added to AFS. This would be an awesome feature to have. Presumably, for each file one would keep an auxiliary one with, say, 4 or 8 bytes of checksum for each 512 bytes block of payload? Or 64 bytes of Hamming codes, allowing single bit error correction and dual bit detection? -- Stephan Wiesand DESY -DV- Platanenallee 6 15738 Zeuthen, Germany
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