How can i make sure my volume is btrfs (or get it's type) and how can I know it's real size in my partition?

Question

I have a volume which I believe to be btrfs, but the partition bearing it has an odd number of blocks and there is a little space left before the next partition.

I'd like to check it's type (btrfs expected) and know the exact space It occupies in my partition (When asking google, I get information about the apparent size vs real size problem related with snapshots, which I don't care about right now)

To make things clearer :

• I'm NOT looking for the size/type of the partition itself, but for the size of the filesystem (the data structure) which should normally be smaller or equal the partition size; and
• I'm also NOT looking for the free space inside the filesystem.

Answer 1

You can use lsblk -f or blkid -p <device> to check for the filesystem type.

To check size of the btrfs filesystem use btrfs filesystem show <mountpoint>. It prints all devices that are part of the btrfs volume and their sizes:

Label: none  uuid: 19e516b2-50bb-4130-9b6e-ee245fb45e43
        Total devices 1 FS bytes used 144.00KiB
        devid    1 size 2.00GiB used 228.75MiB path /dev/sdb

You can see the size of the filesystem on /dev/sdb is 2 GiB. If you are interested in the exact size, use --raw to print sizes in bytes:

Label: none  uuid: 19e516b2-50bb-4130-9b6e-ee245fb45e43
        Total devices 1 FS bytes used 147456
        devid    1 size 2147483648 used 239861760 path /dev/sdb

(Quick check this is really size of the filesystem and not the block device: after shrinking the filesystem with btrfs filesystem resize it now shows devid 1 size 1.90GiB used 228.75MiB path /dev/sdb.)

Answer 2

Show partition size:

parted -l <device> unit s print

You can try command above. <device> is expected to be /dev/sda, /dev/sdb, /dev/mmcblk1, etc.

• unit s means set unit to sector
• print shows disk information

Show filesystem usage:

df

or

df -h

h option of df command makes the format readable for humans. This option will use a unit like G or M.

for Btrfs:

btrfs filesystem df <path>

Show Btrfs filesystem usage:

btrfs filesystem usage <path>

You can replace <path> with like /.

• https://man7.org/linux/man-pages/man8/btrfs-filesystem.8.html