[arch-general] btrfs & Arch

[C Anthony Risinger]

On Wed, Aug 24, 2011 at 12:28 AM, Gour-Gadadhara Dasa <gour at atmarama.net> wrote:
> On Mon, 22 Aug 2011 14:25:52 -0500
> C Anthony Risinger <anthony at xtfx.me> wrote:
>
>> ... tbh, unless you want to get a feel for it, are ready to
>> troubleshoot, or have a specific use-case -- and have some other
>> backup systems in place -- you'll probably just want to roll with "the
>> usual" for now.
>
> Let me say that I'm a bit spoiled with elegant setup I've on FreeBSD with ZFS
> and would like to mimic it on Linux with btrfs.
>
> Machine is connected to UPS and I've tape backup.
>
> However, I'm still not sure how the setup should be for 2 disks in mirror?
>
> With ZFS, I've everything; iow. root, boot & swap in single pool which is then
> mirrored to the 2nd disk which is part of the same pool.
>
> With btrfs, I understand I can avoid using separate /boot and have root on
> btrfs, add two disks as raid-1 under btrfs partition, but wonder whato do in
> regard to swap considering btrfs does not provide swap space?
>
> Does it mean that I'd have to create separate swap partitions on each disk and
> put them into raid-1 array with mdadm and then put the rest of the disk(s) as
> btrfs partion in mirror?

unfortunately you can only do /boot on btrfs if you use a single disk
due to bootloader limitations:

https://wiki.archlinux.org/index.php/Installing_on_Btrfs_root

... details most of the procedure, but it needs to be updated because
until bootloaders and utilities can handle it better, the result is a
PITA to work with ... newer btrfs features like compression render
your system unbootable unless you manually decompress the kernel
image, there is no partition table so you can't modify the disk layout
after the fact, etc etc.  page needs a warning or something.

swap has been disabled in btrfs because it will corrupt it ... btrfs
move blocks around constantly while performing COW and swap
file/partition expects stable address block IIRC -- which btrfs does
not guarantee or even attempt -- so you end up corrupting the FS
*bad*.  using a loopback device + swapfile *should* work, but i don't
know of anyone actually doing it yet :-)

so yeah, you'd need something like `mdadm` to handle the RAID bits.
eventually i hope to get `mkinitcpio-btrfs` updated to do fancy stuff
like a 2-stage kexec boot so you CAN boot from a btrfs array ... but
idk when that will be :-) ... mostly working ATM but time time time
... there's never enough.

after all that, it might be simpler to just use ext4 since your
running softraid anyway ... unless you want to try stuff like
compression and snapshots.

-- 

C Anthony