> If you disagree, please tell us *why* you think snapshots don't solve the > problem.
Three reasons. First of all, unless we have per-file snapshots, there's no way to keep old versions of particularly important files without keeping old versions of everything else. If I have a 4 GB video in my home directory, and my 50 KB file containing finance data, keeping the last version of the 50 KB file (last edited two weeks ago) means keeping the 4 GB file around. Forever, if I never make another change to the 50 KB file. Second, with any rational implementation of file versioning, the end user has control over the number of versions kept for a particular file. Generally snapshots are administratively defined rather than end-user defined, and not at file granularity. Third, snapshots are tied to time, not change. A real-life example: One day I logged into a VAX to test a small program and discovered the Ada compiler wasn't working because it was complaining about an error in its configuration file. It turned out I'd edited that some eight months earlier (two semesters ago) and made an error which had never been caught as I'd finished the course involved. I simply deleted the current (bad) version, reverting to the last good version. Even if I'd had snapshots going back that far, it would have been painful to find which one (if any) had the correct version of the file. Similarly, I can edit a script, test it, find that the change doesn't work, and go back, all within 150 seconds or so. The chances that a snapshot would pick up the previous version in this scenario are low. Technically, these could be seen as arguing against the current *implementation* of snapshots. One can envision per-file, user-configurable snapshots. Those would come close, though the third argument above is still an issue. (I can also imagine a "snapshot only if modified" command which might help there.) That said, do file versions fit into UNIX? I think they could be made to, but they would change existing behavior, which could confuse either users (amply demonstrated in these threads) or applications. (For what it's worth, incidentally, most users don't use the command line, believe it or not....) This message posted from opensolaris.org _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
