Add LVM2 support

[i2]

Two very unrelated requests:

1. Add support a specific use-case which needs having BTRFS inside LVM2
2. LVM2 as an snapshotting alternative to BTRFS (if at all possible!)

[lambdanil]

the second one is especially interesting to me, but I'll have to look into how exactly LVM2 works a bit more

[i2]

Re 2: Even if feasible, this should be an option and not a replacement.

[lambdanil]

yes, I'd keep btrfs as the default

[i2]

Sounds good. I think I read somewhere a while ago that LVM2 snapshotting has caveats.

[I should have probably added this as a discussion piece (option on the right), but all is fine.]

I don't think right now, I have time to investigate option number 2, so I'll leave it to you @CuBeRJAN.

[lambdanil]

alright, I'll look into it!

[i2]

It might be worth looking into integrating snapper in, as it does support LVM snapshots.

[xplshn]

What about AUFS overlays? Same as EasyOS does it with the WoofQ build system. EasyOS is an immutable distro that runs from RAM, at shutdown, you are asked if you want to save the session, it is also encrypted and it is great for using in public computers.

https://easyos.org/