Separate mount options for subvolumes?

Separate mount options for subvolumes?

[Michel Alexandre Salim]

Hello,

It is my understanding that currently, the only difference between
subvolumes and snapshots are that snapshots share a root with an
existing tree, while subvolumes start off empty.

There is an interesting use case difference, though: because a
subvolume by definition cannot share data with other subvolumes, that
frees it up to being mounted with different options (e.g. nodatasum,
nodatacow).

The reason I'm wondering is that I just switched my home directory to
btrfs, and one of my machine is often used for rebuilding RPMs (for
initial testing, before getting it built on a build server). The data
is never kept for a long time, and so checksumming and COW would just
slow things down.

Would this be possible, and if so, is it planned for implementation by 1.0?

Thanks,

-- 
Michel Alexandre Salim

Re: Separate mount options for subvolumes?

[Chris Mason]

On Mon, Sep 14, 2009 at 03:55:39PM -0400, Michel Alexandre Salim wrote:
> Hello,
> 
> It is my understanding that currently, the only difference between
> subvolumes and snapshots are that snapshots share a root with an
> existing tree, while subvolumes start off empty.
> 
> There is an interesting use case difference, though: because a
> subvolume by definition cannot share data with other subvolumes, that
> frees it up to being mounted with different options (e.g. nodatasum,
> nodatacow).
> 
> The reason I'm wondering is that I just switched my home directory to
> btrfs, and one of my machine is often used for rebuilding RPMs (for
> initial testing, before getting it built on a build server). The data
> is never kept for a long time, and so checksumming and COW would just
> slow things down.
> 
> Would this be possible, and if so, is it planned for implementation by 1.0?

It would be possible, and long term we plan on storing a number of
options directly in the root so that you don't have to keep doing mount
-o foo.

-chris