[Zope] backup full instances

Hello, We have several different zope instances running on our servers, and currently the only backup we do is a daily copy of the Data.fs. The main problem with this backup approach is, that the zope instance is not stopped for the backup at all, thus the Data.fs might not be up to date. Is it safe in general to copy Data.fs while the instance is running? Or might I end up with a broken Data.fs, which zope is not able to read at all? And which other ways to you know to backup an entire instance? Maybe sync it with ZEO to another server in realtime? Or use some export method? thanks in advance, jonas