Do I need to stop the service to back up the database? We have several database driven applications using MS SQL Express, Pervasive, MySQL, and some sort of flat file database.  PostgreSQL "may" be added later.

We have backup software that is VSS aware.  I need to backup the database files off the filesystem with regular Windows-based backup software.  We do not have SQL plugins for the backup software.

Do I need to stop the database service before the backup system runs at night, to ensure the database files are in a "consistent" state that can be restored?  Or will the VSS snapshot taken by the backup software allow me to reliably restore data 100% of the time?

I simply need a quick &amp; dirty way of copying the data files with my typical, vss aware, backup software.  Using the SQL plugin would only provide back ups for MS SQL Express anyway.
In SQL Server you do not backup the database's files directly.  You issue a BACKUP command which creates a new file, usually with a .bak extension.  You do not need to stop SQL Server to do this.  It is this new file which is moved to tape &amp; off site.  To restore you will present this .bak file to a RESTORE command.  Here's a previous question on the subject and the Microsoft site.  I imagine the other RDBMSs would work similarly but I claim no expertise with them.  Read the publisher's documentation.

For a flat file system I imagine you would definitely have to stop all write activity to ensure integrity of the data within the files you may hope to restore later.  Again, ask the developers.