Hmmm, that's mean, if the server crash or burn after 5 years, the backup is not realy a backup? you have to look for a equal server and may the same software version?
We will have a feature in this year that will allow you to take the backup "Dynamic Volume" and use with any products being NAS-R3 Enterprise or DSS.
Even if you had a Microsoft server and it burned you would have to rebuild a new server install the backup software (some are very $$ - our backup feature is free) and restore the tapes or vtl or drive. You won't be able to take the MS backup and place on a MAC system either.
You can take our backup and use any Linux system with a free backup program to do a restore if need be. So we do have some flexibility.
Also keep in mind we do offer NDMP .
You could also replicated your data to another NAS-R3 for such issues as you described with disaster recovery procedures with our Data Replication or even Volume Replication with DSS.
Use a Linux and install Bacula. You will have to research how to use the Bacula from within the Linux system. But in the next few releases you wont need to do this .