On Sat, 2008-07-19 at 09:50 -0700, David Woodhouse wrote: > On Sat, 2008-07-19 at 15:21 +0300, Ahmed Kamal wrote: > > Hi, > > Since btrfs is someday going to be the default FS for Linux, and will > > be on so many single disk PCs and laptops, I was thinking it should be > > a good idea to insert some redundancy in single disk deployments. Of > > course it can help with disk failures, since it's obviously a "single" > > disk, but it can help with bit-rot, and with hardware sector read > > errors. To get that we'd need to implement some kind of forward error > > correction, possibly reed solomon code. I am not sure why no > > filesystem seems to implement such scheme, although I believe at the > > hardware level, such schemes are being used (so the idea is > > applicable) ? > > We have implementations of such schemes in lib/reed_solomon/ in the > kernel already. > > I'm quite interested in using btrfs on flash (I mean _real_ flash not > SSDs where they have their own internal pseudo-fs pretending to be a > disk). For that, we'd probably want to use precisely this kind of error > correction. Although it's normal to do it at the block level rather than > the filesystem object level; >
The long term goal is to have the checksum algorithm selectable between a number of choices. For metadata, you have 256 bits to use and for data you can use anything that will fit in a btree block. So, the way to do this for real flash would be to implement the selectable checksum, and then store the sum + whatever error recovery code you want in the checksum item. -chris -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
