> I would like to know whether there's a way of starting a database
> backup using Jaybird from the client.

There is no chance to start backup using type 4 JDBC driver. This should be
possible to do with type 2 JDBC driver, please check test case

org.firebirdsql.ngds.TestJaybirdBackupProblem

how to do this. In JayBird 1.5.x the code is already there, but support for
services is not yet officially released.

> Or do I have to start an external OS command using gbak (not prefered -
> it's OS dependent and requires client installation)? Restoring is
> optional.

Not really needed, but note that type 2 JDBC driver requires client
installation.

Roman