this post was submitted on 28 Mar 2024
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Right way to check free/used storage of btrfs filesystem [SOLVED] (programming.dev)
submitted 7 months ago* (last edited 7 months ago) by unhinge@programming.dev to c/linux@lemmy.ml
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While checking for used and free space in a btrfs subvolume, I'm not getting a consistent value. It's confusing and doesn't help.

  1. What is the correct way to find used/free space?
  2. Why are these values inconsistent (except normal du)?

According to btrfs fi usage /home, 83.21 GiB is used.

Overall:
    Device size:		 149.98GiB
    Device allocated:		 100.07GiB
    Device unallocated:		  49.91GiB
    Device missing:		     0.00B
    Device slack:		     0.00B
    Used:			  83.21GiB
    Free (estimated):		  63.06GiB	(min: 38.10GiB)
    Free (statfs, df):		  63.06GiB
    Data ratio:			      1.00
    Metadata ratio:		      2.00
...

As per btrfs fi df /home, used space is 82.86 GiB, not 83.21 GiB.

Data, single: total=96.01GiB, used=82.86GiB
System, DUP: total=32.00MiB, used=16.00KiB
Metadata, DUP: total=2.00GiB, used=178.61MiB
GlobalReserve, single: total=99.50MiB, used=0.00B

As per btrfs fi du -s /home , used space is 63.11 GiB.

     Total   Exclusive  Set shared  Filename
  63.11GiB    13.64GiB    49.01GiB  /home

While according to du -hs /home, 64GiB is used.

Also, maximum space used should be close to 72 GiB as per btrfs fi du -s / and 73 GiB as per du -hs /, if btrfs fi usage includes all subvolumes . '/home' and '/' are on separate subvolumes.

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[–] unhinge@programming.dev 2 points 7 months ago* (last edited 7 months ago)

Between btrfs filesystem usage / and btrfs filesystem du -s / there's nearly 11GiB difference for used space. ~~I have checked btrfs du -hs <path/to/subvolume> for all subvolume in the filesystem, and total seems to be 72 GiB, hence the confusion. Still I don't know if I'm using the tools properly or something else is at fault here.~~

To correct myself, 11GiB is additional space used by snapshot probably ~~used space difference between btrfs fi usage and btrfs fi du -s / is because of diff between snapshot and parent volume (didn't consider that while adding all used GiB of subvolumes)~~. So btrfs filesystem usage works well to check used/free space.

edit: fix incorrect args; additional space is not diff