Currently, Gerrit's account_patch_reviews database does not get backed up.
This database stores the users' reviewed flag for files in patchsets and as of 2020-07-12 take ~0.5 GB of disk space.
Some people say one should back it up. Others say, one should not bother.
There is no strict need to back it up. In case of disaster, the already reviewed files no longer carry a reviewed marker. But that's about it. The site will come up properly without this database.
So we may be deliberately not backing it up. That's a valid approach. But maybe we should then leave a comment in puppet to mark this as not backed up on purpose to avoid confusion.
(This is unrelated to the recent Gerrit 3.2.2 upgrade. This issue and the H2 database outside of MySQL/MariaDB existed long before our old Gerrit 2.15.14. In fact, on gerrit1001, some parts of the database carry timestamp from 2016)