Ubuntu – Install Ubuntu with BTRFS and more subvolumes

btrfsUbuntu

I want to install an Ubuntu Server 11.10 with a BTRFS filesystem (in a RAID1 way).

The problem is that I can't see the option in the installer to make more subvolumes. The installer creates two by default: @ and @home, and I want to separate also @var @tmp…

Is there any option to do this? Maybe with the shell… but I think the installer doesn't understand the subvolumes feature of btrfs, so you can't mount each partition in each subvolume…

Any idea? 🙂

Best Answer

You have to boot into the live DVD. Then you use the shell to set up your hard drives as you would wish, with mkfs.btrfs (and cryptsetup/LUKS, if you want to do that). Once done you use the installer, which you see as an icon on the desktop, to install into that drive setup. Before shutting down, you will have to mount the new install and edit the fstab correctly for the subvolumes (also cryptab, if you use cryptsetup). Then you chroot ("pivot") into the new install, which allows you to use update-initramfs on that new install. Depending on your drive setup, you may also have to update-grub. Once that's done, you're ready to shutdown, removing the install media, and reboot.

If you have any trouble on reboot, you may have to debug by iteration: reboot into the live DVD, remount, edit, update-initramfs, shutdown, remove media and reboot.

Related Solutions

Linux – Mount two btrfs subvolumes simultaneously

You could define the subvolume a that should act as root as default.
in this case it will automatically be mounted instead of the btrfs root.

Assuming your btrfs tree looks like this

/
|
|----a (subvolume containing / directory)
|
|----b (subvolume containing home directory)

in order to set a as default:

mount /dev/sda1 /mnt
btrfs subvolume create /mnt/a
btrfs subvolume set-default /mnt/a

now you can mount your btrfs filesystem and then the subvolume b

mount -o defaults /dev/sda1 /a
mount -o defaults,subvol=b /dev/sda1 /b

BTRFS unmountable after cold reboot (total_rw_bytes is twice too big)

"Is it safe to call btrfs rescue fix-device-size?"

It's potentially safe, and this is very likely the solution. It "shouldn't" eat your entire volume and several cats. If this BTRFS filesystem has multiple disks (for example, in a BTRFS RAID), I'm suddenly less confident in this assertion.

If you have a block based snapshot mechanism below BTRFS (it looks like you might - is that an LVM volume backing it?) then take a snapshot prior to doing this. You may need to add more physical volumes to that volume group in order to accommodate the snapshot itself depending on how this volume group (if that's what it is) is already allocated. An LVM snapshot will grow in size as data is modified, proportionate to the amount of data modified. An LVM snapshot will also incur a 2x write performance hit while active, so don't keep it around after you're done. This is just so you can roll back if things go very badly.

If it's really important data, do a block based backup to another totally unrelated volume before doing anything - especially if you're not intimately familiar with LVM snapshots or this isn't on LVM. dd is a good command for that.

dd if=/dev/disk/with-btrfs of=/large/enough/volume/backup.img bs=4M

Best Answer

Related Solutions

Linux – Mount two btrfs subvolumes simultaneously

BTRFS unmountable after cold reboot (total_rw_bytes is twice too big)

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