Re: What to do about subvolumes?

[C Anthony Risinger <anthony@extof.me>]

On Wed, Dec 1, 2010 at 12:36 PM, Josef Bacik <josef@redhat.com> wrote:
> On Wed, Dec 01, 2010 at 07:33:39PM +0100, Goffredo Baroncelli wrote:
>
>> Another point that I want like to discuss is how manage the "pivoting" between
>> the subvolumes. One of the most beautiful feature of btrfs is the snapshot
>> capability. In fact it is possible to make a snapshot of the root of the
>> filesystem and to mount it in a subsequent reboot.
>> But is very complicated to manage the pivoting of a snapshot of a root
>> filesystem, because I cannot delete the "old root" due to the fact that the
>> "new root" is placed in the "old root".
>>
>> A possible solution is not to put the root of the filesystem (where are placed
>> /usr, /etc....) in the root of the btrfs filesystem; but it should be accepted
>> from the beginning the idea that the root of a filesystem should be placed in
>> a subvolume which int turn is placed in the root of a btrfs filesystem...
>>
>> I am open to other opinions.
>>
>
> Agreed, one of the things that Chris and I have discussed is the possiblity of
> just having dangling roots, since really the directories are just an easy way to
> get to the subvolumes.  This would let you delete the original volume and use
> the snapshot from then on out.  Something to do in the future for sure.

i would really like to see a solution to this particular issue.  i may
be missing something, but the dangling subvol roots doesn't seem to
address the management of the root volume itself.

for example... most people will install their whole system into the
real root (id=5), but this renders the system unmanageable, because
there is no way to ever empty it without manually issuing an `rm -rf`.

i'm having a really hard time controlling this with the initramfs hook
i provide for archlinux users.  the hook requires a specific structure
"underneath" what the user perceives as /, but i can only accomplish
this for new installs -- for existing installs i can setup the proper
"subroot" structure, and snapshot their current root... but i cannot
remove the stagnant files in the real root (id=5) that well never,
ever be accessed again.

... or does dangling roots address this?

C Anthony
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