RFC for zfs tests.

[jcumming]

This is a work in process. This isn't intended for merging quite yet..

This patchset adds support, documentation, and tests for installing NixOS to a ZFS partition. Booting off of ZFS is probably possible with a sufficient of grub-fu, but currently only separate boot/root is tested.

There is also a new test for running the zfs unit tests.

Dodgy bits:

• I had to bump up the amount of memory for the VMs from 384MiB to 768MiB. Don't know a way around this, but maybe we could isolate it to this test?
• I changed the qemu cache policy for the virtual drives from 'writeback' to 'writethrough', as ztest was failing
• I added 'zfs' to supported filesystems on the ISO. I'm not sure if this makes the ISO distributable (because of the CDDL). This is probably fixable by installing the zfs software/kernel modules before creating the filesystems, but I'm not sure the best way to do that.

[jcumming]

This should probably be wrapped down to 72 columns.

[Shados]

I don't have anything to say regarding the tests, not being sufficiently familiar with NixOS, but on the ISO distribution issue, there's this from the ZOL FAQ (emphasis mine):

The combination of them causes problems because it prevents using pieces of code exclusively available under one license with pieces of code exclusively available under the other in the same binary. In the case of the kernel, this prevents us from distributing ZFS as part of the kernel binary. However, there is nothing in either license that prevents distributing it in the form of a binary module or in the form of source code.

Seeing as you'd only be distributing it as a separate binary module, it looks like it shouldn't be an issue.

On another note, I've been using this set of commits on one of my systems to enable a ZFS root, and it has worked well for me thus far :).

[jcumming]

I think all I really need to do is issue the correct variant of nix-env -i kernelPackages.zfs, and load the modules. Now that I have a fast box with lots of memory, I should be able to fix this up.

@Shados; if you're feeling adventurous, you could try setting up bootable zfs. It was more grub than I could stomach..

[vcunat]

Well, what is the status of this ancient PR?

[jcumming]

I will close this PR, port the tests, and open a new PR.