The database in Spectrum Protect/TSM is absolutely critical to the operation of the backup. The location of the backup copy of every file from every host is stored in that database, and a stale database means loosing backup data. My day job has involved running TSM servers for over 16 years now with many hundreds of TB backed up. I am looking at Duplicati for my home backup and just commenting on what so far I see as a weakness of Duplicati based on my extensive TSM experience.
The fundamentals are if you are using a DB in this manner like TSM and Duplicati then protecting that database for disaster recovery is essential. It would be fair to say Duplicati is lacking in this regard, though it’s also fair to note you are not forking out thousands of $$$ for your backup solution so don’t expect all the same features. I am just pointing out that it is possible.
So how does TSM manage it’s DB backup. Well first thing to note is when the DB is being backed up you can’t backup anything else at the same time. In fact all active backups get paused during the DB backup. TSM being server/client can have many clients backing up to the same server at once all sharing the same database.
The second point to note is that a DB backup is handled separately from a file backup and the backup data is not intermingled with the file backup data. This is where the notion of changes to the Duplicati code come in. That is while the SQLite DB is just a file on the client a DB backup function would be handled separately from the standard file backup. I have zero experience with developing .NET so it would be a very steep learning curve before I could contribute actual code unfortunately.
In TSM land the DB backup history is nothing more than a simple text file that can be read by the TSM server so it can find it’s DB backups for a restore, from where it can then go on to do a restore of the files. Noting due to the client/server nature of TSM this is only necessary should you use the server. If you loose the client it’s much simpler.
For Duplicati I guess the most obvious way would be a method of synchronizing the local SQLite DB with a remote copy. Do backup, then optionally sync SQLite DB with a copy at the remote location.