The z/OS NFS client uses block I/O daemons (BIOD) to perform asynchronous read or write when datacaching is enabled. The biod parameter specifies the number of asynchronous block I/O daemons to use. If there are a lot of users on the NFS client system, it may be advantageous to increase the number of BIODs. The maximum number of BIODs should never exceed two times the number of client system processors. This will avoid excessive TCB switching. Tuning of this parameter should be done with caution. Any change to the biod parameter requires restarting z/OS UNIX.