Difficulty: ★★★☆☆ 
part1
switch from ext4 to btrfs without losing the data 
benefits
- It protects the stick because btrfs works with Copy_on_Write
- It offers the possibility to make automatic snapshots with snapper. This allows you to undo accidental deletion or modification of files within a given period of time. (This is not a substitute for a good backup)
- It offers the possibility to save the files compressed. This increases the capacity and also protects the stick
- After a failed update, you can switch back to the last snapshot (rollback)
- The subvolumes for / and /home are separate, rollback does not result in loss of data
- Even after a rollback, the data from the unsuccessful update (read only) can be accessed. So it can be analyzed well.
disadvantages
- btrfs needs maintenance from time to time
- The rollback is manual work (although only a few commands)
https://btrfs.wiki.kernel.org/index.php/Conversion_from_Ext3/4_and_ReiserFS
Please open and work through one step after the other
Preparation
- Insert our manjaro stick to a “normal” Linux system or a Plug in Linux live system (do not mount).
- Which device is the stick?
- Pay attention to the partitioning and the size.
lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINTS
...
sdz 8:32 1 59,5G 0 disk
├─sdz1 8:33 1 250M 0 part
├─sdz2 8:34 1 1M 0 part
└─sdz3 8:35 1 59,3G 0 part
sdy 8:48 1 14,7G 0 disk
├─sdy1 8:49 1 250M 0 part
├─sdy2 8:50 1 1M 0 part
└─sdy3 8:51 1 14,5G 0 part
Our 64GB stick is /dev/sdz. 3 partitions, 60GB size, 250MB boot partition, 59G data partition - fits. Wherever ‘sdz1’, ‘sdz3’ or ‘z3$’ is used in the following, you have to replace the ‘z’ with the ‘appropriate’ letter.
Always check beforehand whether the ext4 file system is OK
fsck.ext4 /dev/sdz3
e2fsck 1.46.2 (28-Feb-2021)
/dev/sdz3: sauber, 219881/3891200 Dateien, 1312455/15541243 Blöcke
Now convert to btrfs
btrfs-convert /dev/sdz3
create btrfs filesystem:
blocksize: 4096
nodesize: 16384
features: extref, skinny-metadata (default)
checksum: crc32c
free space report:
total: 63656931328
free: 57548845056 (90.40%)
creating ext2 image file
creating btrfs metadata
copy inodes [.] [ 219706/ 219881]
conversion complete
make bootable again (adjust UUIDs)
The UUID and the PARTUUID have changed. We will need these two numbers later. (You can then insert it with copy & paste)
ls -lA /dev/disk/by-uuid |egrep 'z3$'
lrwxrwxrwx 1 root root 10 19. Jun 07:58 1a488830-65f7-4913-bf4d-dfe3f3ab5634 → …/…/sdz3
ls -lA /dev/disk/by-partuuid |egrep 'z3$'
lrwxrwxrwx 1 root root 10 19. Jun 07:58 026eb222-79f0-4dd8-8735-4ea6735f9203 → …/…/sdz3
mount partitions
sudo mkdir -p /mnt/alma/1 /mnt/alma/3
mount -t vfat /dev/sdz1 /mnt/alma/1
mount -t btrfs -o subvol=/,defaults,compress=zstd:9 /dev/sdz3 /mnt/alma/3
Back up grub.cfg and fstab
cp /mnt/alma/1/grub/grub.cfg /mnt/alma/1/grub/grub.cfg.old
cp /mnt/alma/3/etc/fstab /mnt/alma/3/etc/fstab.old
Adapt grub.cfg so that the stick boots
- Show old value
cat /mnt/alma/1/grub/grub.cfg |egrep -o '[0-f]{8}[0-f-]{28}'
d8fb2a88-6bc3-4f79-9ac0-5be115f04ec5
…
- new value should be:
ls -lA /dev/disk/by-uuid |egrep 'sdz3'
lrwxrwxrwx 1 root root 10 19. Jun 07:58 1a488830-65f7-4913-bf4d-dfe3f3ab5634 → …/…/sdz3
- Assemble sed from the above values
sed -i** 's/d8fb2a88-6bc3-4f79-9ac0-5be115f04ec5/1a488830-65f7-4913-bf4d-dfe3f3ab5634/g' **/mnt/alma/1/grub/grub.cfg
- Please check the new value
cat /mnt/alma/1/grub/grub.cfg |egrep -o '[0-f]{8}[0-f-]{28}'
1a488830-65f7-4913-bf4d-dfe3f3ab5634
Customize btrfs layout
btrfs has no layout at all here. I prefer a flat layout (prepared for snapper):
toplevel (volume root directory, not to be mounted by default)
├─@ (subvolume root directory, mount at /)
├─@home (subvolume home directory, mount at /home)
├─@nosnap (subvolume without snapshots, mount at /var/log ...)
├─@snapshots (snapshots of /, mount at /.snapshots)
├─@home.snapshots (snapshots of /home, mount at /home/.snapshots)
└─@ext4_saved (subvolume of saved ext4 filesystem-data, delete later on)
btrfs subvolume create /mnt/alma/3/@
Create subvolume ‘/mnt/alma/3/@’
btrfs subvolume create /mnt/alma/3/@home
Create subvolume ‘/mnt/alma/3/@home’
btrfs subvolume create /mnt/alma/3/@nosnap
Create subvolume ‘/mnt/alma/3/@nosnap’
btrfs subvolume create /mnt/alma/3/@snapshots
Create subvolume ‘/mnt/alma/3/@snapshots’
btrfs subvolume create /mnt/alma/3/@home.snapshots
Create subvolume ‘/mnt/alma/3/@home.snapshots’
mv /mnt/alma/3/ext2_saved /mnt/alma/3/@ext2_saved
mv /mnt/alma/3/home/\* /mnt/alma/3/@home/
mv /mnt/alma/3/[a-z]\* /mnt/alma/3/@/
btrfs subvolume set-default /mnt/alma/3/@
Customize fstab (mount /, /home)
https://www.reddit.com/r/linux/comments/imgler/btrfs_relatime_vs_noatime_huge_performance/
The fstab file on the stick must be adapted to btrfs and the layout. For this we need the PARTUUID of the btrfs partition
ls -lA /dev/disk/by-partuuid |egrep 'sdz3'
lrwxrwxrwx 1 root root 10 19. Jun 07:58 026eb222-79f0-4dd8-8735-4ea6735f9203 → …/…/sdz3
The fstab must be edited by hand. I use mcedit, but nano or vim are just as good. We write the Partuuid in advance at the end of the fstab. Then editing is easier.
ls -lA /dev/disk/by-partuuid |egrep 'sdz3' >> /mnt/alma/3/@/etc/fstab
mcedit /mnt/alma/3/@/etc/fstab
- The line with vfat remains untouched
- The line with ext4 is commented out (#)
- Also the line with “lrwxrwxrwx” where the partuuid is (#)
- With this PARTUUID 2 new lines are created for / and /home
The result looks like this for me:
# UUID=d8fb2a88-6bc3-4f79-9ac0-5be115f04ec5 / ext4 rw,noatime 0 1
# lrwxrwxrwx 1 root root 10 19. Jun 07:58 026eb222-79f0-4dd8-8735-4ea6735f9203 -> ../../sdz3
PARTUUID=026eb222-79f0-4dd8-8735-4ea6735f9203 / btrfs rw,noatime,compress=zstd:9,subvol=@ 0 0
PARTUUID=026eb222-79f0-4dd8-8735-4ea6735f9203 /home btrfs rw,noatime,compress=zstd:9,subvol=@home 0 0
UUID=003C-4A02 /boot vfat rw,noatime,fmask=0022,dmask=0022,codepage=437,iocharset=ascii,shortname=mixed,utf8,errors=remount-ro 0 2
Delete backup of ext4 data (don't forget !)
btrfs subvolume delete -c /mnt/alma/3/@ext2_saved
unmount
umount /mnt/alma/3
umount /mnt/alma/1
