On Sat, Dec 6, 2014 at 4:31 AM, Michael <[email protected]> wrote: > > ZFS's checksums can tell me "Hey, the data you tried to read is no good". I > want to know that before I need to restore from backup.
That's what a scrub is for. And verifying the backup against the current state. Things get easier if the main data is on ZFS as well. > I can't use ZFS for time machine. You can. My TimeMachine store is hosted on a FreeNAS box. It's not as ideal as a directly attached; I definitely see more TM errors over wireless, but I don't think a TimeCapsule would be any better. > I can't control whether the drive's internal buffer is error correcting > memory or not. I can't control if the disk sector was written correctly but > has become unreadable. Don't forget cosmic rays, theft, fire, or flood. Though ZFS is designed to work around the other issues you mentioned. > All I can do is compare what's on the disk with what's on the backup, file by > file. "tmutil compare" can do that, but it will report too many false > positives -- everything modified since the last backup will show as > different, and everything that should not be backed up will show as missing. 'compare' doesn't list excluded files. You're left with files that have changed and I'd think you'd want to know about those. I can't think of a way to determine that a file has changed on disk vs. becoming corrupt on disk vs. becoming corrupt in the backup. fsevents can help narrow it down to the change being in the backup or on disk, but maybe fsevents missed a file, or a bug in fsevents has triggered a false positive / negative. > To have an automated verification, I need to be able to filter to only those > files that should be on the backup and have not changed / do not need to be > backed up again. I don't think you can really have an automated verification. You can get a list of differing files, but you need to inspect the files to determine if there is corruption or not. And if your verification occurs after corruption on disk has been backed up, what are you verifying exactly? You could do things like writing checksum files and comparing against those as well as against the backup, but now you're getting into the territory of implementing your own custom version of a subset of ZFS or some other modern filesystem. It occurs to me that with OpenZFS [1] it'd be possible to format some hunk of your internal hard drive as ZFS and put all your personal files there. Then you can replicate instead of using TimeMachine. [1]: https://openzfsonosx.org > Open Radar: I'm not sure. About half of what I submit is closed as a > duplicate, and I can never see the originals. I have no clue how to see > someone else's bug report, nor how to share mine. You share yours by posting the same content to openradar.appspot.com -- arno s hautala /-| [email protected] pgp b2c9d448 _______________________________________________ MacOSX-talk mailing list [email protected] http://www.omnigroup.com/mailman/listinfo/macosx-talk
