[libvirt] RFC: btrfs storage pool using subvolumes & snapshots

[Daniel P. Berrange]

On Fri, Aug 30, 2013 at 01:57:52AM +0300, Oskari Saarenmaa wrote:
> I wrote an experimental btrfs storage pool which uses subvolumes (and
> optionally snapshots) as storage volumes in LXC domains.  The code is
> available at https://github.com/saaros/libvirt/compare/btrfs-storage but
> it's still missing some features like quotas for the subvolumes
> (currently the capacity definition for volumes is ignored) and doesn't
> have any documentation so far.
> 
> Sample usage:
>   mkdir /virtual; mkfs.btrfs /dev/vdb; mount -t btrfs /dev/vdb /virtual
>   virsh pool-create-as testpool btrfs --target /virtual
>   virsh vol-create-as testpool vanilla 0
>   echo vanilla > /virtual/vanilla/test
>   virsh vol-create-as testpool test 0 --backing-vol vanilla
>   cat /virtual/test/test
>   btrfs subvolume list /virtual
> 
> Does this look like a useful feature and does it make sense to implement
> it as a new storage pool type, or should it be merged into an existing
> one?  I looked at the existing ones and couldn't really figure out how
> to make it fit nicely in any of them.

I'd certainly love to see this added in libvirt. I'm really not sure
about the question fo using an existing pool vs a new pool type. I'll
have to play around with your code to understand it a bit better to
make a recommednation.

> As far as I could tell none of the existing storage pools or volumes
> offered a way to create a new copy-on-write volume for easy use in LXC
> domains using the libvirt API.  With the new btrfs pool I was able to
> replace KVM domains using qcow2 volumes with LXC + btrfs with very
> little changes to the application code.


Daniel
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