Martin posted on Mon, 18 Aug 2014 19:16:20 +0100 as excerpted: > Also, for the file segment being defragged, abandon any links to other > snapshots to in effect deliberately replicate the data where appropriate > so that data segment is fully defragged.
FWIW, this is the current state. The initial attempt at snapshot-aware-defrag was committed to mainline (the kernel release is listed in the wiki's changelog page) but people quickly ran into scaling issues with multi-thousand-snapshot systems as well as quotas that weren't originally expected or, I guess, tested, pre- mainline-merge, so they ended up reverting the snapshot awareness temporarily, until they could come up with something more scalable. I believe they've addressed some of that now, but I'm not sure it's yet scaling the way the original trial suggested it needed to, and snapshot- aware-defrag remains disabled for the time being. So at least currently, defragging isn't snapshot aware, and as a result, if the filesystem is highly fragmented, attempting to defrag will increase space usage substantially as all those snapshot links are broken in ordered to defrag the file on the currently mounted and being defragged snapshot. -- Duncan - List replies preferred. No HTML msgs. "Every nonfree program has a lord, a master -- and if you use the program, he is your master." Richard Stallman -- 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
