Compaq Infortrend Manuale Utente

distributed across two host ports and managed by both
controllers.

! 

Some operating systems do not read multiple LUNs under single
ID.  As diagrammed above, you may have the host channel to
present several IDs and map logical configurations to these IDs.
Each of these IDs can be identified as Primary or Secondary.  As a
rule for most operation systems, each configuration unit will be
mapped to LUN0 under each ID.

Hardware failures can occur.  A simple parity error may sometimes
cause a RAID system to completely hang up.  Having two controllers
working together will guarantee that at least one controller will
survive the catastrophes and keep the system working.  This is the
logic behind having the redundant controllers – to minimize the best
we could the chance of down time for a storage subsystem.

A redundant controller system uses two controllers to manage the
storage arrays.  It requires two controllers to work together and both
must be working normally.  During normal operation, each controller
serves its I/O requests.  If one controller should fail, the existing
controller will temporarily take over for the failed controller until it is
replaced.  The failover and failback processes should be totally
transparent to host and require only minimum efforts to restore the
original configuration.