On Wed, Feb 27, 2008 at 10:42 PM, Marcus Sundman <[EMAIL PROTECTED]> wrote: > Darren J Moffat <[EMAIL PROTECTED]> wrote: > > Marcus Sundman wrote: > > > Nicolas Williams <[EMAIL PROTECTED]> wrote: > > >> On Wed, Feb 27, 2008 at 05:54:29AM +0200, Marcus Sundman wrote: > > >>> Nathan Kroenert <[EMAIL PROTECTED]> wrote: > > >>>> Are you indicating that the filesystem know's or should know what > > >>>> an application is doing?? > > >>> Maybe "snapshot file whenever a write-filedescriptor is closed" or > > >>> somesuch? > > >> Again. Not enough. Some apps (many!) deal with multiple files. > > > > > > So what? Why would every file-snapshot have to be a file that's > > > valid for the application(s) using it? (Certainly zfs snapshots > > > don't provide that property either, nor any other backup-related > > > system I've seen.) > > > > If it isn't how does the user or application know that is safe to use > > that file ? > > Unless the files contain some checksum or somesuch then I guess it > doesn't know it's safe. However, that's unavoidable unless the > application can use a transaction-supporting fs api.
Checksums only tell you the data file is good. If you have a whole load of backups (one every nano-second) and none of them have a good checksum, you are still very screwed. > > Is it okay to provide a snapshot of a file that is corrupt and will > > cause further more serious data corruption in the application ? > > Well, apparently so. That's what zfs snapshots do. That's what all > backup tools do. Sure it would be better to have full transactions in > the fs api, but without that I don't think it's possible to do any > better than "the file might be corrupt or it might not, good luck if > your file format doesn't support corruption-detection". A good backup practice increases (significantly) the likelihood of getting a usable backup. E.g. you quiesce Oracle before you start your backup to make sure that the datafiles you backup are consistent. Still, you are missing the point. What's the point of backing up if you cannot use it for restoring your environment? -- Just me, Wire ... Blog: <prstat.blogspot.com> _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
