Blackdiamond Msm Redundancy; Causes Of Msm Failover And System Behavior - Extreme Networks BlackDiamond 6804 Troubleshooting Manual

Hardware Architecture

BlackDiamond MSM Redundancy

The CPU subsystems on a pair of BlackDiamond MSMs operate in a master-slave relationship.
(See Figure 5.)
Figure 5: BlackDiamond MSM redundancy scheme
MSM64i (A)
CPU
Sub-
system
Fault Tolerant
Switch Fabric
and
MSM64i (B)
System
Management
CPU
Sub-
system
CPU Control Path
Data Path
The master MSM CPU subsystem actively manages the switch and the task of switching packets in the
CPU control (or management) path. The slave MSM CPU subsystem is in standby mode, but is checked
periodically by the master MSM CPU (via EDP) to determine whether it is still available.
The master MSM also guarantees that management operations occur in a synchronized manner. For
example, if you make a configuration change and need to save it, the master MSM ensures that the
configuration is saved to both the master MSM and the slave MSM at the same time. That way, the
updated slave is ready to take over as the master if the master MSM fails.
Despite the master-slave switch management role, the switch fabrics on both MSMs actively switch core
traffic in a load-shared fashion. Load-sharing switches core traffic from different I/O modules.
All MSMs share the control (or management) bus on the backplane, and use it to communicate to each
other and to installed I/O modules to perform system health checks and status polling.

Causes of MSM Failover and System Behavior

A number of events can cause an MSM failover to occur, including:
• Software exception; system watchdog timer expiry
• Diagnostic failure (extended diagnostics, transceiver check/scan, FDB scan failure/remap)
• Hot removal of the master MSM or hard-reset of the master MSM
20
Switching
Fabric
Switching
Fabric
Backplane
I/O Module
I/O Module
I/O Module
I/O Module
I/O Module
I/O Module
I/O Module
I/O Module
DN_028A
Advanced System Diagnostics and Troubleshooting Guide