On martedì 8 novembre 2016 12:38:48 CET, James Pharaoh wrote:
You can't deduplicate a read-only snapshot, but you can create read-write snapshots from them, deduplicate those, and then recreate the read-only ones. This is what I've done.
Since snapper creates hundreds of snapshots, isn't this something that the deduplication software could do for me if I explicitely tell it to do so? I mean momentarily switching the snapshot to rw in order to deduplicate it, then switching it back to ro.
In theory, once this has been done once, it shouldn't have to be done again, at least for those snapshots, unless you want to modify the deduplication. It's probably a good idea to defragment files and directories first, as well.
I can't defragment anything, because it would take too much free space to do so with so many snapshots. Instead, the deduplication software could defragment each file before calling the extent-same ioctl, that would be feasible. Such a way you will not need hilarious amounts of free space to defragment the fs.
It should be possible to deduplicate a read-only file to a read-write one, but that's probably not worth the effort in many real-world use cases.
This is exactly what I would expect a deduplication tool to do when it encounters a ro snapshot, except when I explicitely tell it to momentarily switch the snapshot to rw in order to deduplicate it.
Niccolo' Belli -- 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
