Hi Christian, Paul and Austin, Christian wrote: > However, fstrim still gives me "0 B (0 bytes) trimmed, so that may be > another problem. Is there a way to check if trim works?
Paul wrote: > I've got the same problem. I've got 2 SSDs with 2 partitions in RAID1, > fstrim always works on the 2nd partition but not the first. There are > no errors on either filesystem that I know of, but the first one is > root so I can't take it offline to run btrfs check. Austin wrote: > I'm seeing the same issue here, but with a Crucial brand SSD. > Somewhat interestingly, I don't see any issues like this with BTRFS on > top of LVM's thin-provisioning volumes, or with any other filesystems, > so I think it has something to do with how BTRFS is reporting unused > space or how it is submitting the discard requests. Probably you all suffer from the same problem I had a few years ago. It is a bug in how btrfs implements fstrim. To check whether you are a victim of this bug simply run: # btrfs-debug-tree /dev/whatever | grep 'FIRST_CHUNK_TREE CHUNK_ITEM' where /dev/whatever is a device of your filesystem, and interrupt after the first several output lines with C-c. (Officially the filesystem should be unmounted when running btrfs-debug-tree, but that is not necessary as we only read from it and the relevant data doesn't change very often.) You get something like: item 2 key (FIRST_CHUNK_TREE CHUNK_ITEM 0) item 3 key (FIRST_CHUNK_TREE CHUNK_ITEM 12947816448) item 4 key (FIRST_CHUNK_TREE CHUNK_ITEM 14021558272) ... (This output is from an old version of btrfs-progs. I understand newer version are more verbose, but you should nevertheless easily be able to interpret the output). If the first number different from 0 (here, the 12947816448) is larger than the sum of the sizes of the devices the filesystem consists of, bingo. This has been discussed already in the past and there is a patch. Please see for the patch: http://www.mail-archive.com/linux-btrfs@vger.kernel.org/msg40618.html and for the background: http://comments.gmane.org/gmane.comp.file-systems.btrfs/15597 Kind regards, Lutz Euler -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
