Directory Server 11g Release 1 (11.1.1) supports the compaction of suffixes offline. Online compaction is not supported in this release. If storage space is available, compacting a suffix reduces the size of the database by reorganizing the database keys, and returns the storage space to the filesystem, if possible. Since application data is not processed and based on the way the database keys are managed, it is not guaranteed that the storage space can be reclaimed. Nevertheless database size will not grow.
Stop the server and backup your database before performing this task.