There are three different file locations defined in configuration file of the Mervis DB service that should be backed up. The service is usually configured so that all three paths point to the same folder though.

Simple copy of all files located in the following folders should provide you with usable backup of the data. It is safe to copy the files while the service is running as most files are read only and only logs are appended during the service operation.

Path to infrastructure files (variables, users, state information).
Files are not accessed very often and their size is moderate but in general
it is good to have fast read/write sequential access (better startup times).
<add key="InfrastructureDataPath" value="c:\temp\mervisdb\"/>
Path to log files (persistent log, acceleration permanent files).
Log files are accessed very often for sequential writes.
On server stop and start fast read/write access is welcome.
<add key="LogsPath" value="c:\temp\mervisdb\"/>
Path to permanent data files (historical data).
Writes are rare (only when a new files is produced). Fast sequential and random (to less extent) read access is welcome.
<add key="PermanentFilesPath" value="c:\temp\mervisdb\"/>