Reference Guide

High Availability | 393
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High Availability
High Availability (HA) features are supported only on a stacked S5000 switch; they are not supported on a
standalone S5000.
High availability is a collection of features that preserves system continuity by maximizing uptime and
minimizing packet loss during system disruptions. The features in this collection are:
• High Availability on S5000 Stacks
• Hitless Behavior
• Graceful Restart
• Software Resiliency
• Hot-lock Behavior
High Availability on S5000 Stacks
An S5000 stack has a master and standby management unit that provide redundancy in a similar way to
redundant Route Processor Modules (RPMs). The master unit synchronizes the running configuration and
protocol states so that the system fails over in the event of a hardware or software fault on the master unit.
In such an event, or when the master unit is removed, the standby unit becomes the stack manager and
FTOS elects a new standby unit. FTOS resets the failed master unit: once online, it becomes a member
unit; the remaining members remain online.
For more information on the failover process in an S5000 switch stack, see the Stacking chapter.
Hitless Behavior
Hitless is a protocol-based failover behavior in a stacked S5000 switch that is transparent to remote
systems. In the event of a switch failover, there is no need to notify remote systems of a local state change.
Hitless protocols are compatible with other hitless and graceful restart protocols. Hitless failovers may be
triggered by a software or hardware exception, or a forced failover via the CLI.