On small systems it should never be a problem to use one single PostgreSQL server for all the functions listed above. In the standard installation, the replica manager, the pnfs companion are not activated by default. The billing cell will only write to a file by default. Also, prior to version 1.6.6 of dCache only the pnfs server which does not use PostgreSQL was shipped. In this case, PostgreSQL will only be used if the conversion described in Chapter 19, Moving the pnfs Data from GDBM to PostgreSQL was done.

Whenever the PostgreSQL server is going to be used for another functionality, the impact on performance should be checked carefully. To improve the performance, the functionality should be installed on a separate host. Generally, a PostgreSQL server for a specific funcionality should be on the same host as the dCache cell accessing that PostgreSQL server, and the PostgreSQL server containing the databases for the pnfs server should run on the same host as the pnfs server and the PnfsManager cell of the dCache system accessing it. Accordingly, the pnfs companion and the pnfs server itself will use the same PostgreSQL server.

It is especially useful to use a separate PostgreSQL server for the billing cell.