Re: [ANNOUNCE] Btrfs: a copy on write, snapshotting FS

Chris Mason
2007-06-13T16:38:29Z

On Wed, Jun 13, 2007 at 12:12:23PM -0400, John Stoffel wrote:
> >>>>> "Chris" == Chris Mason <chris.mason@oracle.com> writes:

[ nod ]

> Also, I think you're wrong here when you state that making a snapshot
> (sub-volume?) RO just requires you to set the quota to 1 block. What
> is to stop me from writing 1 block to a random file that already
> exists?

It's copy on write, so changing one block means allocating a new one and
putting the new contents there. The old blocks don't become available
for reuse until the transaction commits.

-chris