lee <l...@yagibdah.de> wrote: > Rich Freeman <ri...@gentoo.org> writes: > > > On Tue, Jan 19, 2016 at 5:22 PM, lee <l...@yagibdah.de> wrote: > >> "J. Roeleveld" <jo...@antarean.org> writes: > >> > >> How does that work? IIUC, when you created a snapshot, any changes you > >> make to the snapshotted (or how that is called) file system are being > >> referenced by the snapshot which you can either destroy or abandon. > >> When you destroy it, the changes you made are being applied to the > >> file system you snapshotted (because someone decided to use a very > >> misleading terminology), and when you abandon it, the changes are thrown > >> away and you end up with the file system as it was before the snapshot > >> was created. > >> > >> In any case, you do not get multiple versions (which only reference the > >> changes made) of the file system you snapshotted but only one current > >> version. > >> > >> Do you need to use a special file system or something which provides > >> this kind of multiple copies when you make snapshots? > >> > > > > And that is exactly what zfs and btrfs provide. Snapshots are full > > citizens. If I create a snapshot of a directory in btrfs it is > > essentially indistinguishable from running cp -a on the directory, > > except the snapshot takes only seconds to create almost entirely > > regardless of size, and takes almost no space until changes are made. > > Later I can delete the snapshot, or delete the original, or keep both > > indefinitely making changes to either. > > Hm, I must be misunderstanding snapshots entirely. > > What happens when you remove a snapshot after you modified the > "original" /and/ the snapshot? You destroy at least one of them, so you > can never get rid of the snapshot in a non-destructive way? > > My understanding is that when you make a snapshot, you get a copy that > doesn't change which you can somehow use to make backups. When the > backup is finished, you can remove the snapshot, and the changes that > were made in the meantime are not lost --- unless you decide to throw > them away when removing the snapshot, in which case you get a rollback. > > To make things more complicated, I've seen zfs refusing to remove a > snapshot and saying that something is recursive (IIRC), and it didn't > make any sense anymore. So I left everything as it was because I didn't > want to loose data, and a while later, I removed this very same snapshot > without getting issues as before. Weird behaviour makes snapshots > rather scary, so I avoid them now. > > There seems to be some sort of relationship between a snapshot and the > "original" which limits what you can do with a snapshot, like the > snapshot is somehow attached to the "original". At least that makes > some sense to me because no real copy is created when you make a > snapshot. But how do you detach a snapshot from the "original" so that > you could savely modify both?
In zfs you can clone the snapshot and it will be independent, but I am new at zfs, so check it out. -- Your life is like a penny. You're going to lose it. The question is: How do you spend it? John Covici cov...@ccs.covici.com