For example, host systems might include computers from IBM, Hewlett-Packard, Sun Microsystems or other vendors, running operating systems such as UNIX or Windows NT. The hosts 22 may communicate with the Symmetrix arrays across any of various input/output (I/O) technologies known in the art and supported by Symmetrix ???Directors??? which handle Symmetric I/O, such as SCSI, Ultra SCSI, ESCON and F