OpenDJ is designed to work with local storage for the database, not for network file systems such as NFS.
High performance storage is essential if you need to handle high write throughput.
The Berkeley Java Edition DB works well with traditional disks as long as the database cache size allows the DB to stay fully cached in memory. This is the case because the database transaction log is append only. When the DB is too big to stay cached in memory, however, then cache misses lead to random disk access, slowing OpenDJ performance.
You might mitigate this effect by using solid-state disks for persistent storage, or for file system cache.
Regarding database size on disk, if you have sustained write traffic then the database grows to about twice its initial size on disk. This is normal, and due to the way the database manages its logs. The size on disk does not impact the DB cache size requirements.
