RAM 

1-2 GB for evaluation purposes 

Minimum 2 GB for production servers 

Local disk space 

300 MB disk space for binaries. By default, binaries installed from native packages are placed in /opt on UNIX® systems. For evaluation purposes, an additional 2 GB local disk space for server software might be sufficient.

If you are using Directory Server, consider that entries stored in Directory Server use local disk space. Directory Server does not support logs and databases installed on NFS-mounted file systems. Sufficient space should be provided for the database on a local file system in, for example, /var/opt or /local. For a typical production deployment with a maximum of 250,000 entries and no binary attributes such as photos, 4 GB might be sufficient.

Directory Server may use more than 1.2 GB of disk space for its log files. This should be taken into account that 4 GB storage space is only for the databases, not the logs. 

Directory Server supports SAN disk storage. Before using SAN disk, you need to understand the layout and the design of the disk because the write performance of the system is affected if many applications simultaneously access data from the same disk.