On Tue, Jul 6, 2010 at 10:29 AM, Arne Jansen <sensi...@gmx.net> wrote: > Daniel Carosone wrote: >> Something similar would be useful, and much more readily achievable, >> from ZFS from such an application, and many others. Rather than a way >> to compare reliably between two files for identity, I'ld liek a way to >> compare identity of a single file between two points in time. If my >> application can tell quickly that the file content is unaltered since >> last time I saw the file, I can avoid rehashing the content and use a >> stored value. If I can achieve this result for a whole directory >> tree, even better. > > This would be great for any kind of archiving software. Aren't zfs checksums > already ready to solve this? If a file changes, it's dnodes' checksum changes, > the checksum of the directory it is in and so forth all the way up to the > uberblock. > There may be ways a checksum changes without a real change in the files > content, > but the other way round should hold. If the checksum didn't change, the file > didn't change. > So the only missing link is a way to determine zfs's checksum for a > file/directory/dataset. Am I missing something here? Of course atime update > should be turned off, otherwise the checksum will get changed by the archiving > agent.
What is the likelihood that the same data is re-written to the file? If that is unlikely, it looks as though znode_t's z_seq may be useful. While it isn't a checksum, it seems to be incremented on every file change. -- Mike Gerdts http://mgerdts.blogspot.com/ _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
