Reference Guide

High Availability | 383
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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 Dell
Networking OS elects a new standby unit. Dell Networking OS 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.