The Site Recovery Manager Server requires its own database, which it uses to store data such as recovery plans and inventory information.
Site Recovery Manager provides an embedded vPostgreSQL database that requires fewer steps to configure than an external database. The embedded vPostgreSQL database supports a full-scale Site Recovery Manager environment.
Each Site Recovery Manager site requires its own instance of the Site Recovery Manager database.
If you are updating Site Recovery Manager to a new version, you can use the existing database. Before you attempt an upgrade, make sure that both Site Recovery Manager Server databases are backed up. Doing so helps ensure that you can revert back to the previous version after the upgrade, if necessary.
For the list of database software that Site Recovery Manager supports, see the Compatibility Matrices for Site Recovery Manager 8.5 at https://docs.vmware.com/en/Site-Recovery-Manager/8.5/rn/srm-compat-matrix-8-5.html.