Re: RFC: Btrfs snapshots feature proposal for Fedora 13

[Goffredo Baroncelli <kreijack@gmail.com>]

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On Tuesday 17 November 2009, Chris Ball wrote:
> Hi,
> 
> I've written up a draft of an Fedora 13 feature proposal for
> filesystem rollback using Btrfs snapshots that are automatically
> created by yum:
> 
>    https://fedoraproject.org/wiki/Features/SystemRollbackWithBtrfs
> 
> It'd be great to get feedback on whether this is a good idea, and how
> the UI interaction should work.  We're also discussing it in this
> fedora-devel thread:
> 
>    http://thread.gmane.org/gmane.linux.redhat.fedora.devel/123695
> 
> Some comments I've got already received, from the thread:
> 
> * People want the UI to allow independent active snapshots per
>   filesystem (i.e. btrfs /home is the live filesystem, and btrfs / is
>   an older snapshot).

On the basis of some empirical tests, I discovered that in btrfs a snapshot 
doesn't doens't affect the other subvolume(s). If / (root) and /home are 
different subvolumes, a snapshot of the / (root) doesn't affect the /home 
content, and viceversa. 

So if the root and the /home directory (or better the userS directories) are 
separate volumes, you have the required behavior.

> 
> * Several people think that the ZFS Time Slider patches to nautilus¹
>   look good, and want that for btrfs.  Sounds plausible, but I'm
>   more interested in first working on ways to let developers feel
>   comfortable upgrading to the development version of Fedora each
>   day with the possibility of reverting.
> 
> * Instead of inventing a new system-config-blah, this should probably
>   be part of Palimpsest².
> 
> * Perhaps we should encourage people using the Fedora installer with
>   btrfs to create a rootfs separate to their /home, so that they can
>   rollback rootfs snapshots without affecting their homedir.

On the basis of my tests, I think that is sufficient to create a volume for 
the root ('/') and on for the /home (or a specific subvolume for every user). 
Then it is possible to snapshot and "time sliding" every subvolume without 
affecting the others.

I would like to add a my comment: in btrfs I think that "snapshot" (for the 
btrfs snapshot) is not the best name. I think that a better term is "branch". 

For example the btrfs snapshot capability may be used not only for recovering 
from a mistake, but also may be used for maintaining different 
configurations...

> Thanks!
> 
> - Chris.

BR
G.Baroncelli
> 
> ¹:  http://blogs.sun.com/erwann/entry/zfs_on_the_desktop_zfs
>     http://blogs.sun.com/erwann/entry/time_slider_screencast
>     http://blogs.sun.com/erwann/entry/new_time_slider_features_in
> 
> ²:  http://library.gnome.org/users/palimpsest/stable/intro.html.en
> -- 
> Chris Ball   <cjb@laptop.org>
> One Laptop Per Child
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