Compaq StorageWorks HSG60 ACS Solution Software V8.6 for Sun Solaris Installation and Configuration Guide

Fibre Channel: Considerations for Both Loop and Fabric Environments 6–3
NOTE: This chapter does not attempt to answer questions of loading or performance.
Storage
The term Storage, as used in this chapter, is a RAID Array. Specifically, RAID arrays that
are supported by the Compaq HSG60 family of controllers. This controller supports all of
the standard RAID set configurations in a loop or fabric environment. These configuration
elements are discussed in the following sections.
A Special Note on Controller Pairs
(Active-Passive vs. Active-Active)
In dual controller systems, most controller pairs are configured for redundancy which
means that the controllers are bound together in a such a way that if one controller fails,
the second controller will automatically service the I/O stream, protecting the integrity of
the data. Typically, this redundancy is created for failover protection. Failover can be
implemented as either Active-Passive or Active-Active.
In Case 1, (shown in Table 6–1) all I/O would be loaded on a single controller, controller
A, and in the event of a failure the Passive channel would handle the I/O from the failed
controller. Having the load on a single controller is not a benefit. It is a drawback to the
processing power of the controller pair.
In Case 2, (shown in Table 6–2) both I/O channels are protected and are able to distribute
the processing load over both controllers.
The fact that one controller is active while the other controller is passive frequently leads
to a misnomer of Active-Passive to describe the redundant pair. The reason that this is a
misnomer is the fact that the description is referring to a single controller and not the
controller pair.
Table 6–1 Case 1: Active-Passive (Describes the controller pair)
Channel 1 - Active Channel 2 - Active Controller A Primary Ch 1,
Primary Ch 2
Channel 1 - Passive Channel 2 - Passive Controller B Standby Ch 1,
Standby Ch 2