[lxc-users] zfs snapshot point

[Chris Burroughs]

On 07/07/2014 10:21 AM, Serge Hallyn wrote:
> Quoting Chris Burroughs (chris.burroughs at gmail.com):
>> Currently when using lxc-snapshot the snapshot point is the rootfs
>> dataset. (so something like /lxc/foo/rootfs)  I'm trying to
>> understand why the dataset doesn't also include the config file (so
>> /lxc/foo/). Isn't that file also needed to reconstitute a snapshot,
>> or is that information duplicated somewhere inside the rootfs?
>
> It's not duplicated inside the rootfs, and on the one hand what you
> suggest can make sense.  However, consider that the rootfs of a
> system container often can be directly used to boot a full virt vm
> (i.e. kvm) or even bare metal host, and consider things like lvm-,
> loop-, and qemu-nbd-backed containers.
>
> That's not to say we couldn't make btrfs and zfs behave differently,
> but doing that will complicate things at the higher levels, i.e.
> toolsets which are using the lxc api to provide containers for
> something (a build farm, whatever) when they are switched from one
> backing store type to another.
>

Thanks, the take-advantage-of-the-tool vs 'do the same thing as the 
other tool' tradeoff makes sense.

For ZFS a 3rd option might be making both /lxc/foo and /lxc/foo/rootfs a 
dataset.  That way ZFS folks can snpapshot at will while rootfs being 
treated more or less the same as everything else.