HP StorageWorks XP48 Configuration Manual page 28

2. For all LUNs, determine the device number as follows (once Open VMS
sees the XP disks):
Open VMS device name ($1$dgaxxx), where xxx = (CU*256) +
LDEV (Convert the LDEV number from hex to decimal)
Example: For an XP LUN with a CU of 2 and an LDEV of 59:
LDEV = 59 hex = 89 decimal
Open VMS device identifier = 2*256+89 = 601
The example LUN is presented to Open VMS as $1$dga601.
The figure below shows an example of the Command View LUN
Managment display that you use to perform LUN mapping.
28 HP StorageWorks Disk Array XP Operating System Configuration Guide: OpenVMS