> In that case the only thing you can do is close FB - copy
> file - restart FB.
>
> Its not a model I would go for, but its safe.

I agree...

> It sounds as if you need some means of telling the users
> that the database is unavailable, which is what switching to
> exclusive mode is supposed to do. But I don't see how you
> can prevent a downtime, since making changes and bringing a
> new database back up will take time, during which you can
> not allow any other work on the old copy.

Yes, but I'm looking from the other side of the coin. I can tell users not
to log in between these hours, but that doesn't mean I haven't overlooked
some other program that connects to the database. I would like my upgrade
to fail gracefully if someone is currently connected. It should then set
this exclusive mode that you mentioned... Can you tell me more about that?

During the upgrade period, including a backup and restore, the users would
not be able (allowed) to use the system.