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Just a few questions about Btrfs:
mk_btrfs_subfolder /home (or whatever the command is), instead of having to make a new empty subvolume and copying everything over?The commands to do the above would be good but not necessary, just yes/no will be fine and I can Google how.
Yes you have to mount it, and if you want to convert a directory into a subvolume what you can do is create a snapshot using
btrfs subvolume snapshot <name of subvolume containing folder> @new_subvol
Then you could go into the subvolume and delete everything other than @new_subvol/home for instance and move everything in home to the root of the new subvolume with something like
mv @new_subvol/home/* @new_subvol
Then you could delete the original directory and move the newly created snapshot into its place.
At least not at the moment.
Can I easily convert an existing directory into a subvolume? (i.e. if I want to make "/home" a separate subvolume can I just go mk_btrfs_subfolder /home (or whatever the command is), instead of having to make a new empty subvolume and copying everything over?
For large subvolumes the least bad way of doing this is by creating the subvolume as a snapshot and then cleaning things up. This avoids actually copying any file data though it does mean a bunch of meta data updates that would be unnecessary if this was supported natively.
Andrew mentions this in his answer but doesn't give a complete worked example so here is one. I take a slightly different approach from him moving the old directories out of the way first so I can create the subvolumes in their final locations.
cd /build/
mkdir xxxx
mv *-rpi-staging xxxx
btrfs subvolume snapshot /build /build/wheezy-armhf-rpi-staging
btrfs subvolume snapshot /build /build/jessie-armhf-rpi-staging
btrfs subvolume snapshot /build /build/stretch-armhf-rpi-staging
btrfs subvolume snapshot /build /build/buster-armhf-rpi-staging
cd /build/wheezy-armhf-rpi-staging/
find -maxdepth 1 ! -name xxxx ! -name . -exec rm -rf {} +
(shopt -s dotglob; mv -- xxxx/wheezy-armhf-rpi-staging/* . )
rm -rf xxxx
cd /build/jessie-armhf-rpi-staging/
find -maxdepth 1 ! -name xxxx ! -name . -exec rm -rf {} +
(shopt -s dotglob; mv -- xxxx/jessie-armhf-rpi-staging/* . )
rm -rf xxxx
cd /build/stretch-armhf-rpi-staging/
find -maxdepth 1 ! -name xxxx ! -name . -exec rm -rf {} +
(shopt -s dotglob; mv -- xxxx/stretch-armhf-rpi-staging/* . )
rm -rf xxxx
cd /build/buster-armhf-rpi-staging/
find -maxdepth 1 ! -name xxxx ! -name . -exec rm -rf {} +
(shopt -s dotglob; mv -- xxxx/buster-armhf-rpi-staging/* . )
rm -rf xxxx
Notes on this worked example.
Can I easily convert an existing directory into a subvolume? (i.e. if I want to make "/home" a separate subvolume can I just go mk_btrfs_subfolder /home (or whatever the command is), instead of having to make a new empty subvolume and copying everything over?
I had a specific version of this problem: I have a couple of top-level btrfs subvolumes on my file system that are snapshotted by a utility called snapper on a particular schedule. Unfortunately this can create quite a lot of bloat when it comes to oft-changing directories, of which I had many that I wanted to exclude.
At initial setup, excluding particular paths from snapshots is easy: just make a new btrfs subvolume at the path in question. Unfortunately, it's a bit more complicated once you have a running system.
I thought this wouldn't be too hard to script, and so I started a little bash script. And of course that little script quickly grew to almost 100 lines, as I started to handle different kinds of input, file locks, permissions, etc.
If you have a similar problem (snapper-managed btrfs filesystem that you'd like to prune), I invite you to use (at your own risk): https://github.com/billwanjohi/snapper-exclude/blob/master/snapper-exclude.sh
