Q-Logic SN0054651-00 F manual SAN or Cluster Configuration, Host Host Y

System Overview Configurations

S

SAN or Cluster Configuration

Figure 2-3shows 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).

Host X

Host Y

Adapter

A

0	1	2	3	4	Target
					Devices

Adapter

B

Figure 2-3 SAN or Cluster Configuration

If Figure 2-3represents 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 0–1and mask devices 2–4, and host Y is configured to see devices 2–4and 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 2-3represents 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).

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