On Tue, 2009-04-28 at 16:04 +0200, Thomas Glanzmann wrote: > Chris, > what blocksizes can I choose with btrfs?
Right now the blocksize can only be the same as the page size. For this external dedup program you have in mind, you could use any multiple of the page size. > Do you think that it is > possible for an outsider like me to submit patches to btrfs which enable > dedup in three fulltime days? Three days is probably not quite enough ;) I'd honestly prefer the dedup happen entirely in the kernel in a setup similar to the compression code. But, that would use _lots_ of CPU, so an offline dedup is probably a good feature even if we have transparent dedup. You'd have to: Wire up a userland database that stores checksums and points to file,offset tuples Make the ioctl to replace a given file extent if and only if the file contents match a given checksum over a range of bytes. The ioctl should be able to optionally do a byte compare of the src and destination pages to make 100% sure the data is really the same. Make another ioctl to report on which parts of a file have changed since a given transaction. This will greatly reduce the time spent scanning for new blocks. It isn't painfully hard, but you're looking at about 3 weeks total time. -chris -- 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
