On 2015-08-06 03:23, Duncan wrote:
> Martin posted on Wed, 05 Aug 2015 09:06:40 +0200 as excerpted:
>
>> [W]hat is the penalty of a subvolume compared to a directory? From a
>> design perspective, couldn't all directories just be subvolumes?
>
> In addition to the performance issues mentioned by others, there's at
> least one further practical reason as well.
>
> Snapshots stop at subvolume boundaries.  It's thus quite useful to use
> subvolumes to delineate the limits of the snapshot, saying, in effect,
> snapshot this dir (which happens to be a subvol not just a normal dir)
> recursively, but don't snapshot the subtree starting with this nested
> subdir (which again is a (different) subvol).
>
And for some people, this is very useful functionality.  I use it to 
specifically exclude subsets of trivially reproducible data from backups 
(for example, I always clone public git repositories into individual 
subvolumes, and keep my local copy of the Portage tree on a separate one 
(when it isn't on a separate filesystem that is)).