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Forum Discussion
Defrag can consume free space on disks.
Being a newbie I have been trawling the forum to increase my knowledge of how things work. I was shocked to find this not necessarily obvious information. If it isn't obvious to me, then it isn't to ...
There already are several places in the forum where we point out that CoW shouldn't be enabled in cases where files are frequently modified. This is just one example (the file was fragmented in the first place because CoW was enabled and it was modified).
I believe 6.1.9 was adjusted so the snapshots are not defragmented. If a file in the main share is defragmented because of CoW then either you skip defragging that file, or you no longer share blocks with the snapshot (increasing space). There are no other options. There is a btrfs "snapshot aware" defrag option, but it created problems so the btfrs folks turned it off.
Note also that when the volume becomes full the NAS should automatically start deleting snapshots to free up space.
In general it is a bad idea to let the volume become full, and it is best to fix that by deleting files (or snapshots) before doing other stuff.
Perhaps edit your original post to add a condition: Files in the share are frequently modified.
I believe 6.1.9 was adjusted so the snapshots are not defragmented. If a file in the main share is defragmented because of CoW then either you skip defragging that file, or you no longer share blocks with the snapshot (increasing space). There are no other options. There is a btrfs "snapshot aware" defrag option, but it created problems so the btfrs folks turned it off.
Note also that when the volume becomes full the NAS should automatically start deleting snapshots to free up space.
In general it is a bad idea to let the volume become full, and it is best to fix that by deleting files (or snapshots) before doing other stuff.
Perhaps edit your original post to add a condition: Files in the share are frequently modified.
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