Antonio Vargas wrote: > On 8/4/06, Edward Shishkin <[EMAIL PROTECTED]> wrote: > >> Hans Reiser wrote: >> > Edward Shishkin wrote: >> > >> > >> >>Matthias Andree wrote: >> >> >> >> >> >>>On Tue, 01 Aug 2006, Hans Reiser wrote: >> >>> >> >>> >> >>> >> >>>>You will want to try our compression plugin, it has an ecc for every >> >>>>64k.... >> >>> >> >>> >> >>> >> >>>What kind of forward error correction would that be, >> >> >> >> >> >> >> >>Actually we use checksums, not ECC. If checksum is wrong, then run >> >>fsck - it will remove the whole disk cluster, that represent 64K of >> >>data. >> > >> > >> > How about we switch to ecc, which would help with bit rot not >> sector loss? >> >> Interesting aspect. >> >> Yes, we can implement ECC as a special crypto transform that inflates >> data. As I mentioned earlier, it is possible via translation of key >> offsets with scale factor > 1. >> >> Of course, it is better then nothing, but anyway meta-data remains >> ecc-unprotected, and, hence, robustness is not increased.. >> >> Edward. >> >> > >> >> >> >> and how much and >> >> >> >> >> >>>what failure patterns can it correct? URL suffices. >> >>> >> >> >> >>Checksum is checked before unsafe decompression (when trying to >> >>decompress incorrect data can lead to fatal things). It can be >> >>broken because of many reasons. The main one is tree corruption >> >>(for example, when disk cluster became incomplete - ECC can not >> >>help here). Perhaps such checksumming is also useful for other >> >>things, I didnt classify the patterns.. >> >> >> >>Edward. >> >> >> >> > > > Would the storage + plugin subsystem support storing >1 copies of the > metadata tree? > > I suppose....
What would be nice would be to have a plugin that when a node fails its checksum/ecc it knows to get it from another mirror, and which generally handles faults with a graceful understanding of its ability to get copies from a mirror (or RAID parity calculation). I would happily accept such a patch (subject to usual reservation of right to complain about implementation details).
