Hi all!

I have a Debian stable server with two hdds in a md RAID which contains an encrypted ext-4 filesystem.

sda          8:0    0   2.7T  0 disk
├─sda1       8:1    0     1G  0 part                    
│ └─md0      9:0    0  1023M  0 raid1 /boot             
├─sda2       8:2    0   2.7T  0 part                    
│ └─md2      9:2    0   2.7T  0 raid1                   
│   └─mdcrypt                                           
│          253:0    0   2.7T  0 crypt /                 
└─sda3       8:3    0     1M  0 part
sdb          8:16   0   2.7T  0 disk                    
├─sdb1       8:17   0     1G  0 part
│ └─md0      9:0    0  1023M  0 raid1 /boot             
├─sdb2       8:18   0   2.7T  0 part
│ └─md2      9:2    0   2.7T  0 raid1                   
│   └─mdcrypt
│          253:0    0   2.7T  0 crypt /                 
└─sdb3       8:19   0     1M  0 part

I’d like to migrate that over to BTRFS to make use of deduplication and snapshots.

But I have no idea how to set it up since BTRFS has its own RAID-1 configuration. Should I rather use the existing MD array? Or should I take the drives out of the array, add encryption and then add the BTRFS RAID inside that?

Or should I do something else entirely?

  • UnfortunateShort
    6•3 months ago

    If I had to do encrypted btrfs RAID from scratch, I would probably:

    1. Set up LUKS on both discs
    2. Unlock both
    3. Create a btrfs partition on one mapper
    4. Add the other with btfs device add /path/to/mapper /path/to/btrfs/part
    5. Balance with btrfs balance start -mconvert=raid1 -dconvert=raid1 /path/to/btrfs/part
    6. Add LUKS’ to crypttab, btrfs partition to fstab and rebuild/configure bootloader as necessary

    In that scenario, you would probably want to use a keyfile to unlock the other disc without rentering some password.

    Now, that’s from the top of my head and seems kinda stupidly complicated to me. iirc btrfs has a stable feature to convert ext4 to btrfs. It shouldn’t matter whatever happens outside, so you could take your chances and just try that on your ext volume

    (Edit: But to be absolutely clear: I would perform a backup first :D)

    • Björn TantauOP
      1•3 months ago

      Thanks, sounds good. I need the running system, so I’d first set up BTRFS on one disc, test it and then add the other disc.