Restore UFS snapshot

[Roland Smith]

On Mon, May 28, 2007 at 05:15:19PM +1000, Ian Smith wrote:
> 
> I share Roland's concern about the reliability of any new code designed
> to accomplish the 'full rollback' desired, but of course anything would
> have to undergo incredibly rigorous testing before it would be allowed
> anywhere near even -CURRENT I'm sure, same as softupdates/snapshots has. 
> 
> That said, I think it is worthwhile finding out whether this is even
> possible with the amount of data and metadata saved in snapshots to
> accomplish their existing utility (which I still find pretty awesome,
> and despite re-reading that section again several times, mysterious ..)

It should be possible. All the data that is needed is there. But I do
think it will be definitely non-trivial. 

For one thing, you'll have to block all other changes from userland to
the target filesystem while restoring the snapshot. And you'll have to
update other snapshots as well. Seems like a big can of worms to me.

> I guess contacting Marshall McKusick might be the quickest way to find
> out whether there's sufficient metadata available to do that; he'd know
> off the top of his head, I'm sure.  So should several other people, I
> guess, but more likely those frequenting -fs, -hackers, maybe -arch? 

Excellent idea.

> It may even be possible, assuming restoration of a filesystem to its
> state in a snapshot is possible at all, to first save all subsequent
> changes in its present state to another snapshot, or a snapshot-like
> thing, to allow 'rollforward' again, perhaps .. that would be cute.

If you take a snapshot just before you restore the older one, you could
do that.

Roland
-- 
R.F.Smith                                   http://www.xs4all.nl/~rsmith/
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