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SAN or Cluster Configuration
Figure 2-3 shows a simple storage area network (SAN) configuration consisting of
two hosts (X and Y). Each host has an adapter that connects to a common set of
five target devices (0–4).
Figure 2-3 SAN or Cluster Configuration
If Figure 2-3 represents a SAN of unrelated hosts, then each host is configured to
recognize a different set of devices. This configuration can be made at the target
device level (called target masking) where host X is configured to see devices 0–1
and mask devices 2–4, and host Y is configured to see devices 2–4 and mask
devices 0–1. Alternatively, this configuration can be made at the logical unit
number (LUN) level (called LUN masking), where hosts X and Y recognize the
devices but each has a different set of LUNs masked on the device.
If Figure 2-3 represents a cluster of two hosts, then the hardware setup is the
same; however, for the software configuration, each host is configured to
recognize the same set of devices. Cluster software must determine (arbitrate)
which host accesses which devices at any time. For example, both hosts can be
configured to recognize all targets, but cluster software determines that host X is
the preferred host and owns the devices (unless cluster software determines that
host X is down and host Y takes over).
Host X
A
B
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Target
Devices
Host Y
Adapter
Adapter