On 02/19/2012 02:09 PM, Hugo Mills wrote:

You don't need to unmount the subvolume. Linux allows you to mount a
filesystem in multiple places at one. With the ability to mount
subvolumes separately in btrfs, this means that you can mount the top
level (subvolid=0) somewhere temporarily without having to unmount
anything else. Hugo. 

Thanks for the clarification!

Andrew