You can enable a server instance to restart at system boot time by using the dsadm command. For example, use the dsadm enable-service command on Solaris 10 and Windows systems. On other systems, use the dsadm autostart command. If you did not install from native packages, refer to your operating system documentation for help ensuring the server starts at system boot time.
When possible, stop Directory Server with the dsadm command, or from DSCC. If the Directory Server is stopped abruptly during system shutdown, there is no way to guarantee that all data has been written to disk correctly. When Directory Server restarts, it must therefore verify the database integrity. This process can take some time.
Furthermore, consider using a logging option with your file system. File system logging generally both improves write performance, and also decreases the time required to perform a file system check. The system must check the file system when the file system is not cleanly unmounted during a crash. Also, consider using RAID for storage.