Technical data

Planning a Subsystem 1–27
Restricting Host Access by Offsets
Offsets establish the start of the range of units that a host connection can access. However,
depending on the operating system, hosts that have lower offsets may be able to access the
units in the specified range.
NOTE: All host connections to the same host computer must be set to the same offset.
For example:
In Figure 1–14, assume all host connections initially have the default offset of 0. Giving
all connections access to host BLUE, an offset of 120 will present unit D120 to host
BLUE as LUN 0. Enter the following commands:
SET BLUE1A1 UNIT_OFFSET=120
SET BLUE1B1 UNIT_OFFSET=120
SET BLUE2A2 UNIT_OFFSET=120
SET BLUE2B2 UNIT_OFFSET=120
Host BLUE cannot see units lower than its offset, so it cannot access any other units.
However, the other two hosts can still access D120 as LUN 20 if their operating system
permits. To restrict access of D120 to only host BLUE, enable only host BLUE’s access,
as follows:
SET D120 DISABLE_ACCESS_PATH=ALL
SET D120 ENABLE_ACCESS_PATH=(BLUE1A1,BLUE1B1,BLUE12A2,BLUE2B2)
NOTE: Compaq recommends that you always provide access to only specific connections. This
way, if new connections are added, they will not have automatic access to all units. See
“Restricting Host Access by Disabling Access Paths,” page 1–23.