Sun Microsystems StorEdge 3000 Series, Best Practices Manual

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Chapter 6 Using Multiple Expansion Units in High Capacity Configurations 49
Connecting Five Expansion Units
This high-capacity configuration using five expansion units requires the
configuration of RAID channels 4 and 5 as drive channels. This restricts host
connections to RAID channels 0 and 1, affecting supported host configurations. Use
four expansion units or fewer when possible.
Note –
Other “daisy-chained” cable connections are possible that do not require
reconfiguring RAID channels 4 and 5 as drive channels. However, these connections
introduce a single point of failure where the failure of an expansion unit can render
another expansion unit unusable, making them unacceptable as a best practice
where high availability is an objective.