On Wed, Jan 16, 2013 at 5:17 PM, Sage Weil <[email protected]> wrote: > On Wed, 16 Jan 2013, Gregory Farnum wrote: >> I'm not familiar with the interfaces at work there. Do we have a free >> 32 bits we can steal in order to do that stuffing? (I *think* it would >> go in the NFS filehandle structure rather than the ino, right?) > > Right, there is at least 8 more bytes in a standard fh (16 bytes iirc) to > stuff whatever we want into. > >> We would need to also store that information in order to eventually >> replace the anchor table, but of course that's much easier to deal >> with. If we can just do it this way, that still leaves handling files >> which don't have any data written yet ? under our current system, >> users can apply a data layout to any inode which has not had data >> written to it yet. Unfortunately that gets hard to deal with if a user >> touches a bunch of files and then comes back to place them the next >> day. :/ I suppose un-touched files could have the special property >> that their lookup data is stored in the metadata pool and it gets >> moved as soon as they have data ? in the typical case files are >> written right away and so this wouldn't be any more writes, just a bit >> more logic. > > We can also change the semantics, here. It could be that you have to > specify the file's layout on create, and can't after it was created. > Otherwise you get the directory/subtree's layout. We could store the pool > with the remote dentry link, for instance, and we could stick it in the > fh. So the <ino, pool> is really the "locator" that you would need. > > That could work...
I'm less a fan of forcing users to specify file layouts on create since there aren't any standard interfaces which would let them do that, so a lot of use cases would be restricted to directory-level layout changes. Granted that covers the big ones, but we do have a non-zero number of users who have learned our previous semantics, right? -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
