Dual Active Controllers - nStor Corporation Ultra S2S User Manual

Dual Active Controllers

A dual-active (active-active) fault-tolerant configuration is provided when two
CR8e subsystems, each with Ultra S2S RAID Controllers are installed. This
configuration allows two separate host systems continuous concurrent access to
data. Refer to the installation chapter for diagram and setup information, and the
configuration chapter for software configuration.
Should a fault occur in one controller, the other controller detects the failure and
assumes operations for the failed controller. When the failed controller is
subsequently removed and replaced with a functioning controller, the active
functioning controller detects the presence of the new controller and relinquishes
its assumed responsibilities to the new controller. This process is known as a
fail-over and fail-back. Write cache coherency is maintained with the disk drives
during this process.
The following requirements must be met to establish a dual-active controller
environment:
both controllers must have the same amount of memory
both controllers must be at the same firmware level
all disk SCSI channels must be connected one-to-one
Performance
The advantage gained by the dual-active configuration is an additional margin of
fault tolerance. However, when operating in a dual-active mode and one
controller fails, the performance of the remaining single controller is somewhat
degraded from that of a one controller in a separate environment.
Introduction
7
Dual Active Controllers