On 11/24/2010 11:57 PM, cwillu wrote:
On Wed, Nov 24, 2010 at 5:29 PM, Gordan Bobic<gordan@xxxxxxxxxx> wrote:
On 11/24/2010 10:07 PM, David Nicol wrote:
I've been thinking about this for a while, from a perspective of how
to make it work by allocating i-node numbers from a global pool, but
yesterday I realized that offering the feature would be a bad idea
because it violates the semantics of file systems.
I will be happy to expand on that point if anyone disagrees with it.
One thing I would like to see is copy-on-write hard-links. The hard-links
that span snapshots should be possible, but they should be copy-on-write,
i.e. as soon as hard-linked file that spans snapshots is written, the
snapshot that wrote it should have it's own forked copy henceforth.
There are sym-links, hard-links, and ref-links. Cross device symlinks
are trivial. Cross device hardlinks are evil. Cross device ref-links
are just plain smart (and are at least partitially implemented in
btrfs; does bcp work across subvolumes?). :)
Last time I asked a similar question, there was no equivalent thing to
COW hard-links, across snapshots or otherwise. Hard-links spanning
physical devices don't make sense. Hard-links spanning snapshots,
however, do. In fact, I would intuitively expect that a snapshot
contains only COW hard-links which would get COW-ed from both the head
and the snapshot.
Gordan
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