Compaq RAID ARRAY 3000 EK-SMCPO-UG. C01 - Manual (Page 36)

2-2 RAID Array 3000 Pedestal Storage Subsystem Hardware User’s Guide
Compaq Confidential – Need to Know Required
Writer: Bob Young Project: RAID Array 3000 Pedestal Storage Subsystem Hardware User’s Guide Comments:
Part Number: EK-SMCPO-UG. C01 File Name: c-ch2 RAID Array Controller.doc Last Saved On: 12/4/00 1:51 PM
The controller has two Single Inline Memory Module (SIMM) connectors for
up to 64 MB of cache memory. The SIMM connectors form a mirrored pair
when the controllers are configured in a redundant controller configuration;
otherwise they are fully accessible by the controller. In a redundant controller
setup, both controllers must have identical cache configurations and the total
usable cache (per controller) will be half the amount installed. Thus, in a
single controller setup, the maximum usable cache is 64 MB while a redundant
setup has a maximum usable cache of 32 MB (per controller).
There are two configurations for redundant pairs of controllers: Active/Active
Failover mode and Active/Passive Failover mode. In Active/Active Failover,
each controller in the redundant pair has one active SCSI host port and one
passive SCSI host port. Redundancy Groups (Virtual LUNs) can be mapped
only to one active host port and are not accessible from the passive port or the
other controller (that is partitioned model).
In Active/Passive Failover, one controller in the redundant pair has both SCSI
host ports active and the other controller is in a standby passive mode.
Redundancy Groups (Virtual LUNs) can be mapped to either SCSI host port or
to both as in the single controller model.
In both cases, a single controller failure will not affect the subsystem because
the surviving controller will take over.