On Sat, Jul 01, 2017 at 01:41:43PM +0200, Marian Beermann wrote: > Hi > > > > I'm planning to use this reflink feature for instant local snapshots > > > and then use my backup software of choice, borg, to keep a long time > > > history of my work on a remote server. Since borg stores data in a > > > dedup fashion I can also backup the reflink snapshots and they won't > > > take additional space. The only drawback is that today borg need to > > > hash all the files found in a reflink directory in order to find out > > > about dedup blocks. I asked a question on the borg mailing list > > > https://github.com/borgbackup/borg/issues/2743 and apparently it > > > won't be an issue to add a feature to support XFS in order to > > > identify the physical extents. Is rmapbt required for that? > > > > borgbackup will probably need to call the GETFSMAP ioctl, which won't > > land until 4.12. On xfs, rmapbt is needed to supply data block > > ownership info, which is what borgbackup (and bees, and...) say they > > want to be smarter about dedup. > > My understanding so far was that FIEMAP would be sufficient to query the > extents associated with a file. Shouldn't this be sufficient to know > whether two files on the same file system refer to the same data? Not necessarily -- FIEMAP provides physical offset into a device but does not actually identify which one, which is a problem on multi-device filesystems such as btrfs and XFS. IIRC btrfs creates a virtual physical offset space consisting of all the devices one after the other, but then you have to know /that/ mapping too. GETFSMAP by contrast tells you which device and where on that device. --D > > Cheers, Marian > -- > To unsubscribe from this list: send the line "unsubscribe linux-xfs" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-xfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
