On Thu, Oct 11, 2007 at 09:49:51AM -0700, Matthew Ahrens wrote: > Pawel Jakub Dawidek wrote: > > On Thu, Oct 11, 2007 at 10:47:44AM +0100, Robert Milkowski wrote: > >> Hello Matthew, > >> > >> Thursday, October 11, 2007, 9:10:13 AM, you wrote: > >> > >> MA> Robert Milkowski wrote: > >>>> I haven't looked into details but in theory one should be > >>>> able to copy/move a file within the same datapool between datasets > >>>> without having to actually copy data blocks... or maybe there's some > >>>> detail which actually makes it hard to implement... > >> MA> Once a block is referenced by multiple filesystem, it is nontrivial to > >> MA> determine when it can be freed. > >> > >> In a way multiple snapshots are separate file systems, or clones... > >> What's the difference? However I'm sure you right... > > Well, snapshots are nontrivial too. See > > http://blogs.sun.com/ahrens/entry/is_it_magic > > > Snapshot and clones are not autonomous datasets. A clone has always a > > parent, you can use 'zfs promote' to switch the relatioship, but you > > cannot make them independent, AFAIK. > > > > To Matthew: As I understand it, Robert was talking more about moving the > > blocks to another dataset, not creating a hardlink-like situation - only > > one dataset will reference the blocks after the move. > > Well, he said "copy/move". "copy" implied to me that both filesystems would > reference the same blocks. And even if it is just "move", you still have the > issue of snapshots from the original filesystem referencing it. Changing the > snapshots so they no longer reference the file? Also nontrivial.
I'm sorry for trying to be too helpful:) I understand it's not trivial, but beeing able to reference the same block from different datasets would be a really nice feature to have. The functionality discussed above if only one example. Another example would be block aggregation (which has its own name I can't recall right now), so we can run a thread once a day that frees duplicated blocks and make datasets to point at one copy only. -- Pawel Jakub Dawidek http://www.wheel.pl pjd at FreeBSD.org http://www.FreeBSD.org FreeBSD committer Am I Evil? Yes, I Am! -------------- next part -------------- A non-text attachment was scrubbed... Name: not available Type: application/pgp-signature Size: 187 bytes Desc: not available URL: <http://mail.opensolaris.org/pipermail/zfs-code/attachments/20071011/b14cca9b/attachment.bin>
