User`s guide

2 – System Overview
Configurations
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2.2.4
RAID Configuration and LUN Masking
Figure 2-4 illustrates the interaction of a host adapter alternate with a LUN alternate
in a RAID subsystem. Two hosts (X and Y) are connected to a fabric, which is
simplified for this diagram. Also on the fabric is a RAID subsystem with dual
controllers (left and right) containing eight LUNs.
Figure 2-4. RAID Configuration and LUN Masking
This is a generic example of a RAID configuration. Many, but not all, RAID systems
operate in this manner. Details of the configuration are described in the following
paragraphs.
■ All hosts and storage devices are connected to a common fabric. Details of fabric
configuration are not important, except to note that all hosts and HBAs can
connect to all storage devices. Depending on the fabric, some devices may
appear on the local loop and/or as fabric devices.
■ Hosts X and Y must be configured to recognize different target devices or else
risk overwriting each other’s data. The SANblade Manager application must be
run on each host to configure devices as enabled (with a preferred and alternate
path assigned to each device) or disabled.
■ If hosts X and Y are cooperating in a cluster, they can be configured so that both
recognize a particular device. In this case, clustering software and the clustered
application must determine which host is permitted to write to the device.
■ Host Z can be added to this configuration. SANblade Manager supports up to
30 hosts. The only limiting factor is that SANblade Manager must be run on each
host in turn.
■ The RAID system offers eight LUNs, numbered 0–7. The RAID system typically
has its left and right controllers operating in an active/active manner, with half
the LUNs available on each controller.