Hi! I’m learning how to use btrfs and I need some advice.

One one of my desktop, I made the mistake of creating 2 partitions, one for /(root) and one for home. Both are btrfs. I didn’t know that I could use subvolumes so that they could share the same physical space.

My question: How can I merge the root and home btrfs partitions into only 1 partition that would use btrfs subvolumes?

I’m looking for something like that:

  • Partition1 (btrfs)
    • subvolume 1: @root (mounted to /)
    • subvolume 2: @home (mounted to /home)
  • Partition 2, 3, 4…

My current setup:

  • 1 physical hard drive (1 TB), shown as sda below
  • The partitions I want to merge are sda7 and sda8
  • That computer is an iMac also running MacOS so it has a few other partitions that I should not touch
$ lsblk
NAME   MAJ:MIN RM   SIZE RO TYPE MOUNTPOINTS
sda      8:0    0 931,5G  0 disk 
├─sda1   8:1    0   200M  0 part /boot/efi
├─sda2   8:2    0 371,1G  0 part 
├─sda3   8:3    0 619,9M  0 part 
├─sda4   8:4    0   600M  0 part 
├─sda5   8:5    0  1023M  0 part 
├─sda7   8:7    0 422,9G  0 part /home
└─sda8   8:8    0 135,1G  0 part /
sdb      8:16   1     0B  0 disk 
sr0     11:0    1  1024M  0 rom  

$ blkid
/dev/sda4: UUID="d970eea2-142b-3f1c-9650-5e496d1e9b4b" BLOCK_SIZE="4096" LABEL="Linux HFS+ ESP" TYPE="hfsplus" PARTLABEL="Linux HFS+ ESP" PARTUUID="eab00592-b96d-4ecb-b2e9-816c95eaf860"
/dev/sda2: UUID="6a26963c-eabb-3e42-9e8d-8677a8282b61" BLOCK_SIZE="4096" LABEL="DD Macintosh" TYPE="hfsplus" PARTLABEL="DD Mac" PARTUUID="8257316c-1fd7-4885-bf2b-7e99557acd85"
/dev/sda7: UUID="22f5e59e-8509-484a-92d5-e7dc03bb70cd" UUID_SUB="78a998f5-db55-4a31-9506-afe548ec8d5e" BLOCK_SIZE="4096" TYPE="btrfs" PARTLABEL="Mint Home" PARTUUID="20b6c31d-5e2d-416f-beb3-faa295af67df"
/dev/sda5: UUID="587b0093-4b64-468a-9a01-b933630d184b" BLOCK_SIZE="4096" TYPE="ext4" PARTUUID="a47a3fbf-534a-435d-8916-0f83edebf296"
/dev/sda3: UUID="d0c171e8-572d-39f9-8bdc-38f33744a19a" BLOCK_SIZE="4096" LABEL="Recovery HD" TYPE="hfsplus" PARTLABEL="Recovery HD" PARTUUID="c9d0673b-bb2e-4322-9bf9-c661f7de6856"
/dev/sda1: LABEL_FATBOOT="EFI" LABEL="EFI" UUID="67E3-17ED" BLOCK_SIZE="512" TYPE="vfat" PARTLABEL="EFI System Partition" PARTUUID="d30954cb-b9b6-40fa-9202-a18cf146f7df"
/dev/sda8: UUID="7027382a-4369-4276-b916-9997c1007e5b" UUID_SUB="3e516464-dee1-4bda-9621-29591d54dc2d" BLOCK_SIZE="4096" TYPE="btrfs" PARTLABEL="Mint root" PARTUUID="f2fdb8cc-54fd-46c8-bf1f-85954c1dc363"
  • Atemu@lemmy.mlM
    1·
    5 months ago

    You cannot merge them in any automated fashion. You have to manually copy one into the other.

    btrfs provides some tools here though; you could use btrfs send | btrfs receive to transfer the subvolumes for instance.

    You’d transfer all of your subvolumes in the root partition over to the “home” partition and then adjust your fstab accordingly. After a rebuild of the initrd, your system should boot into the root subvol of the formerly “home” partition. Once that works, you can delete the old root partition and extend the new combined partition.

    • narF@lemmy.caOPEnglish
      1·
      5 months ago

      Can I do this while the system is running? I guess it would be safer to boot to a liveUSB before attempting this?

      Also, what do you mean by “After a rebuild of the initrd” ? That’s something I have to do after editing fstab? How do I do that?