Ds400 Failover - IBM TotalStorage DS300 Best Practices Manual

Green LEDs
On
Off
Off
Green and amber LEDs alternate flashing twice per second
Off
Each of the two Fibre Channel ports (FC0 and FC1) has a unique world wide port
name (WWPN). The management port (ETH0) is used only to access the
controller to make configuration changes and administer the unit.

3.4.4 DS400 failover

All logical drives are seen on all 4 FC ports on a dual controller on DS400.
However, logical drives can only be active on two of those ports at a time. Logical
drives are configured with a "preferred path" and an "alternate path". A DS400
controller will initiate a failover from the preferred to the alternate path any time
the Fibre Channel link goes down on a Fibre Channel port, or the alternate
controller goes offline for some reason. When this failover occurs, the logical
drives will go into a transition state as the array ownership changes. The Device
Specific Module (DSM) will monitor the logical unit numbers (LUNs) until they
change into either a passive state or active state. Once this occurs, the DSM will
issue a command to select the currently active path.
DSM
The Device Specific Module is a major part of the DS400 failover mechanism. A
DSM is the "personality" module that is loaded by the Microsoft MPIO driver to
handle customer failover calls. It is provided by a third party vendor (Qlogic for
the DS400) to implement the actual device moves. A DSM is provided to
differentiate each storage device. Multiple DSMs may be loaded for different
storage device types, but only one instance of MPIO is required. Each DSM
should claim only its own storage device. The DSM provided with the DS400 only
works with the DS400.
A DSM will function only if the Microsoft MPIO driver is installed as well. A DSM
can be thought of as a low level driver talking directly to the hardware. The MPIO
driver is the failover mechanism that builds and manages the path definitions.
Amber LEDs
Off
On
Flashing twice per second
Flashing once per second
Indication
Online (normal operation)
Link established (transitory
condition)
Loss of synchronization
FC chip fault
Beacon
Chapter 3. Components overview
51