Of course, a full featured SQL-database would be the most flexible. The best-known open-source options are MySQL
. Arguably, MySQL is more widely used, has more information available on the internet and is easier to use, than PostgreSQL. On the other side, PostgreSQL is probably more reliable/robust.
For local-disk database-libraries (no direct networking support, very fast, but more difficult to use), Berkeley DB
come to mind. CDB has a 4Gb limit per database, and only source
-distribution is allowed, but can be expected to be robust and fast.
Just files on you ReiserFS, would be a bad idea, if you're serious about lots of data and still having good performance.
From the information you posted, and assuming you're not afraid of some bare-metal programming, I'd think my choice would be Berkeley DB