Ubuntu – btrfs and missing free space

btrfscompressiondisk-usagefilesystem

I converted my ext4 partition to btrfs and deleted the save subvolume after doing so. Then I enabled the compression (lzo) of the filessystem in the fstab file and everything is correct so far.

Then I forced the compression of all files using the defragmentation command with the parameter -c that the new compression is applied to all files.

While doing so, I noticed that my ssd got completly filled up – before I had 6gigs of free space. No I got nothing left.

easteregg@x201s:~$ btrfs fi df /
Data: total=50.00GB, used=49.17GB
System: total=32.00MB, used=4.00KB
Metadata: total=24.50GB, used=9.86GB

and

easteregg@x201s:~$ df -ha
Filesystem        Size  Used Avail Use% Mounted on
/dev/sda1          75G   60G  852M  99% /

So now. How can I regain my free space. I expected to gain more space because of the lzo compression. And now!

The fs is correctly mounted.

easteregg@x201s:~$ mount
/dev/sda1 on / type btrfs (rw,noatime,ssd,compress=lzo)

Any ideas how to fix this issue?

Best Answer

I know this question is old - but as of today the balance command solves this stuff:

During conversion a lot of space will be allcoated to move stuff to it. Once it is allocated, it will not show up as "free" or "unallocated" anymore. To fix this simply start a balance

btrfs balance start "path"

you can also tell the balance command, to only balance chunks, which are used for acertain percentage - like 0% which would mean the chunks are empty:

btrfs balance start "path" -dusage=0 -musage=0

parameter -d means options for the data. parameter -m means options for the metadata.

play with the balance command, it should help.

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Ubuntu – Unable to mount secondary BTRFS filesystem to specific subvolume

Btrfs filesystems do not interact with each other, so you cannot mount the @media subvolume on /dev/sd{b,c}1 because the @media subvolume is currently on /dev/sda1, and you get a cross-device error when you try to snapshot /mnt/media to /mnt/media_snap because /mnt/media is on /dev/sd{b,c}1 whereas /mnt/media_snap is on /dev/sda1.

Instead of having the @media subvolume on the /dev/sda1 btrfs filesystem, you want to create an @media subvolume on the btrfs filesystem on /dev/sd{b,c}1:

sudo mount /dev/sdb1 /mnt/media/
sudo btrfs subvol create /mnt/media/@media
sudo umount /mnt/media/
sudo mount -o subvol=@media /dev/sdb1 /mnt/media/

You can create snapshots of /mnt/media/, but you can place the snapshot only on the /dev/sd{b,c}1 filesystem. So you can create a read-only snapshot like this:

sudo btrfs subvol snap -r /mnt/media/ /mnt/media/<snapshot_name>

But I recommend placing each snapshot of a subvolume outside the subvolume itself, because this simplifies things when you need to revert to a snapshot. To do this, you will need to mount the root of the /dev/sd{b,c}1 filesystem:

sudo mkdir /mnt/media_root/
sudo mount -o subvol=/ /dev/sdb1 /mnt/media_root/
sudo btrfs subvol snap -r /mnt/media_root/@media/ /mnt/media_root/<snapshot_name>

Ubuntu – Mounting BTRFS, no space available

Finally found the solution here at the "Balance cannot run because the filesystem is full" paragraph

Turns out the metadata was full and I had to add an empty device in order to rebalance the FS. No idea why this happened.

Best Answer

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