Arch Linux

pentad

Member

Registered: 2023-06-13

Posts: 6

Btrfs Resize Help / Clarification

I'm still somewhat new dealing with btrfs and after reading the wiki I still have questions about the best solution to my issue:

My current ssd (4TB) is running out of space (see the full btrfs filesystem usage / at the end of this message).

Current stats:

Device size:            3.73TiB
Device allocated:        969.02GiB
Device unallocated:  2.78TiB

If I am reading that correctly I have 2.78TiB unused. So, can I execute this command:

btrfs filesystem resize max /   to allocate the rest of the space?

If so:
    -Can I do this while the system is running?
    -Do I need to do anything else after executing this command (Balance?)

If not:
    -What would you recommend?
   

Thank you for your time in reading this!

** btrfs filesystem usage / **

Overall:
    Device size:           3.73TiB
    Device allocated:         969.02GiB
    Device unallocated:           2.78TiB
    Device missing:             0.00B
    Device slack:             0.00B
    Used:             825.92GiB
    Free (estimated):           2.89TiB    (min: 1.50TiB)
    Free (statfs, df):           2.89TiB
    Data ratio:                  1.00
    Metadata ratio:              2.00
    Global reserve:         512.00MiB    (used: 0.00B)
    Multiple profiles:                no

Data,single: Size:933.01GiB, Used:817.35GiB (87.60%)
   /dev/mapper/luks-2f3ddd75-cead-49b3-a4b4-3a73529c2587     933.01GiB

Metadata,DUP: Size:18.00GiB, Used:4.29GiB (23.81%)
   /dev/mapper/luks-2f3ddd75-cead-49b3-a4b4-3a73529c2587      36.00GiB

System,DUP: Size:8.00MiB, Used:128.00KiB (1.56%)
   /dev/mapper/luks-2f3ddd75-cead-49b3-a4b4-3a73529c2587      16.00MiB

Unallocated:
   /dev/mapper/luks-2f3ddd75-cead-49b3-a4b4-3a73529c2587       2.78TiB

tcloud

Member

Registered: 2025-04-23

Posts: 2

Re: Btrfs Resize Help / Clarification

Just tested this out in a VM with a LUKS encrypted root btrfs partition by booting the latest arch.iso.

Disclaimer: Proper backups are crucial before carrying out any disk operations as there is always a chance for data loss.

1. determine which partition to work on

root@archiso ~ # lsblk
NAME   MAJ:MIN RM   SIZE RO TYPE MOUNTPOINTS
loop0    7:0    0 841.4M  1 loop /run/archiso/airootfs
sr0     11:0    1   1.2G  0 rom  /run/archiso/bootmnt
vda    254:0    0    60G  0 disk 
├─vda1 254:1    0     2G  0 part 
└─vda2 254:2    0    28G  0 part 

root@archiso ~ # blkid --match-token TYPE="crypto_LUKS" --output device
/dev/vda2

2. perform a resize on that partition (ensure you work on the whole disk)

root@archiso ~ # parted /dev/vda resizepart 2 100%
Information: You may need to update /etc/fstab.

3. unlock the partition

root@archiso ~ # cryptsetup open /dev/vda2 root
Enter passphrase for /dev/vda2: 
cryptsetup open /dev/vda2 root  7.26s user 0.14s system 224% cpu 3.300 total

4. mount the luks volume to resize

root@archiso ~ # mount -o compress=zstd /dev/mapper/root /mnt
<...NO_OUTPUT...>

5. resize the btrfs filesystem

root@archiso ~ # btrfs filesystem resize max /mnt
Resize device id 1 (/dev/mapper/root) from 27.98GiB to max
WARNING: the new size 0 (0.00B) is < 256MiB, this may be rejected by kernel

6. verify the size change

root@archiso ~ # btrfs filesystem usage /mnt     
Overall:
    Device size:		  57.98GiB
    Device allocated:		   3.52GiB
    Device unallocated:		  54.46GiB
    Device missing:		     0.00B
    Device slack:		   3.50KiB
    Used:			   2.39GiB
    Free (estimated):		  55.22GiB	(min: 27.99GiB)
    Free (statfs, df):		  55.22GiB
    Data ratio:			      1.00
    Metadata ratio:		      2.00
    Global reserve:		   5.94MiB	(used: 0.00B)
    Multiple profiles:		        no

Data,single: Size:3.01GiB, Used:2.25GiB (74.79%)
   /dev/mapper/root	   3.01GiB

Metadata,DUP: Size:256.00MiB, Used:71.88MiB (28.08%)
   /dev/mapper/root	 512.00MiB

System,DUP: Size:8.00MiB, Used:16.00KiB (0.20%)
   /dev/mapper/root	  16.00MiB

Unallocated:
   /dev/mapper/root	  54.46GiB

And to answer your questions:
Q: Can I do this while the system is running?
A: Unknown, but I can attest that the above method worked for me.

Q: Do I need to do anything else after executing this command (Balance?)
A: Someone else can chime in here, but I don't see a reason to balance if you are just extending a single drive.

pentad

Member

Registered: 2023-06-13

Posts: 6

Re: Btrfs Resize Help / Clarification

Thank you tcloud for the amazing post!!  I followed it to the letter and I believe btrfs has the entire drive space now, but my home directory is still nearly full.

Besides information from the terminal I have also included four screenshots so you can see what I am seeing (they are at the bottom of post):

-- Gpated: Space allocated to btrfs partition
-- btrfs assistant: Also reports the additional space
-- drive properties: Also reports space
-- qdirstat: Show my home directory near full

Do I have to resize the @home subvolume now that the partition has additional space?   Thank you again for the help!

lsblk below shows the drive as 3.7TB and the nvme1n1p2 is also 3.7TB which I think means the space is allocated to btrfs

** lsblk **
NAME                                      MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINTS
zram0                                     252:0    0  62.5G  0 disk  [SWAP]
nvme1n1                                   259:0    0   3.7T  0 disk 
├─nvme1n1p1                               259:1    0   300M  0 part  /boot/efi
└─nvme1n1p2                               259:2    0   3.7T  0 part 
  └─luks-2f3ddd75-cead-49b3-a4b4-3a73529c2587
                                          253:0    0   3.7T  0 crypt /home
                                                                     /var/cache
                                                                     /var/log
                                                                     /root
                                                                     /srv
                                                                     /var/tmp
                                                                     /
nvme0n1                                   259:3    0 476.9G  0 disk 
└─nvme0n1p1

Here sudo btrfs filesystem usage / shows that 2.89TB is unallocated though:

** sudo btrfs filesystem usage / **
Overall:
    Device size:           3.73TiB
    Device allocated:         851.02GiB
    Device unallocated:           2.89TiB
    Device missing:             0.00B
    Device slack:             0.00B
    Used:             704.30GiB
    Free (estimated):           3.01TiB    (min: 1.56TiB)
    Free (statfs, df):           3.01TiB
    Data ratio:                  1.00
    Metadata ratio:              2.00
    Global reserve:         512.00MiB    (used: 0.00B)
    Multiple profiles:                no

Data,single: Size:815.01GiB, Used:695.97GiB (85.39%)
   /dev/mapper/luks-2f3ddd75-cead-49b3-a4b4-3a73529c2587     815.01GiB

Metadata,DUP: Size:18.00GiB, Used:4.16GiB (23.12%)
   /dev/mapper/luks-2f3ddd75-cead-49b3-a4b4-3a73529c2587      36.00GiB

System,DUP: Size:8.00MiB, Used:112.00KiB (1.37%)
   /dev/mapper/luks-2f3ddd75-cead-49b3-a4b4-3a73529c2587      16.00MiB

Unallocated:
   /dev/mapper/luks-2f3ddd75-cead-49b3-a4b4-3a73529c2587       2.89TiB

Screenshots:

tcloud

Member

Registered: 2025-04-23

Posts: 2

Re: Btrfs Resize Help / Clarification

> ...my home directory is still nearly full.
If you are referring to the QDirStat output, I believe that is a representation of total space. You could check upstream to see why the tool doesn't report a percentage out of your available drive space.

> Do I have to resize the @home subvolume now that the partition has additional space?
Negative. You would only need to adjust quotas on the subvolumes if you had them. You do not appear to have enabled quotas.

> Here sudo btrfs filesystem usage / shows that 2.89TB is unallocated though:
This is unused space, not unassigned.