this post was submitted on 28 Mar 2024
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That's just used data. The global used metric likely incorporates metadata etc. too. System aswell as the GlobalReserve are probably accounted as fully used as they're, well, reserved.
Likely compression or inline extents. btrfs only reports apparent size to
du
and friends unfortunately.Your home has a lot of shared extents which indicates to me that you have at least one snapshot of it.
You also wrote 13.6GiB of new data to your home since the snapshot. Assuming a similar amount of data was deleted/overwritten since, that would add up to 76GiB. If there's perhaps one or two more snapshots, that would explain the rest.
Snapshots are "free" only so long as you don't write or delete any data in the origin.
Thanks that helped. I have one snapshot of home. ~~Size of diff between btrfs subvolume and~~ Additional space used by snapshot is 11GiB (probably) and
btrfs fi du -s /
is 72GiB, making 83GiB (closer tobtrfs fi df /
).WDYM by "diff"?
Also forgot to mention but if you want to know what's taking how much space on your btrfs, try
btdu
. It uses a sampling-based approach and will therefore never be 100% accurate but it should be quite accurate enough after a little bit.just comparing the subvolume with its snapshot with
btrfs send -p /example/subvol /snapshot/of/example/subvol >examplediff.btrfs
.From
man btrfs-send
Thanks for btdu, it seems useful as 'btrfs fi du' probably doesn't account for compression, will check it out sometime.
Note that the diff does not necessarily correlate with the amount of data that changed, not how much additional space the snapshot takes.
You are right. I shouldn't have used diff. I'll fix that
Also, incremental changes from subvolume to its snapshot might be incorrect as that will be new data added to subvolume, rather that old data deleted from subvolume while still present in snapshot. I'll have to check carefully.