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Bug#840248: debian-installer: Add btrfs subvolume setting for snapshot

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Control: tags -1 pending

On Mon, Oct 10, 2016 at 09:22:14AM +0900, Hideki Yamane wrote:
>  debian-installer can format disk with btrfs now, but it is NOT appropriate
>  setting with btrfs. We can just format partion with btrfs but cannot create
>  btrfs "subvolume" at that time.
>  Subvolume is a bit special idea, you can slice one btrfs partion to some 
>  subvolume and can set quota for each subvolume, also mount directory and
>  get snapshot for each.
>  So, I'll propose debian-installer to add btrfs subvolume setting menu or
>  add subvolume setting like SUSE by default.

Hi Hideki,

Thank you for the reminder!  I've been planning to do this work for
quite some time.  (
https://lists.debian.org/debian-boot/2016/04/msg00277.html )

So far, the plan is to default to simple @rootfs and @home subvolumes,
because I've read that backing up OpenSUSE systems is cumbersome with
all of those subvolumes, and also because of the KISS principle; That
said, one will have the flexibility to choose this style, if desired.
I absolutely agree that, for example, there needs to be a mechanism in
place to allow configuration of a separate subvol for /var/www and
/var/database_of_choice at the time a Debian system is installed.

The second half of better Debian btrfs support is better
documentation. ( https://wiki.debian.org/Btrfs )  To the best of my
knowledge, the following is still applicable:

As a consequence, per-subvolume btrfs mount options set in the
installer would not be honoured, because the fstab mount option for
@rootfs are applied to all other subvolumes .  The three workarounds
are 1) Create a separate physical partition for @nodatacow_subvol.  2)
chattr +C the mountpoint, relying on the application's own COW and
checksumming implementation.  3) Disable the application's COW and
checksumming implementation and rely on btrfs'.

I'll try to having something ready for testing by Oct 24th, with a
hard deadline of Nov 1st.


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