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PowerConnect B-Series FCX Configuration Guide 173
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PowerConnect B-Series FCX hitless stacking
5
Hitless stacking default behavior
Hitless stacking is disabled by default. When disabled, the following limitations are in effect:
• If a failover occurs, every unit in the stack will reload
• Manual switchover is not allowed. If the CLI command stack switch-over is entered, the
following message will appear on the console:
Switch-over is not allowed. Reason: hitless-failover not configured.
• Internal switchover resulting from a priority change is blocked until the entire stack is reloaded
or hitless stacking is enabled. A priority change will trigger an election, but the newly-elected
winner will not immediately assume its role. For more information, refer to “Displaying pending
device roles” on page 174.
• If there is no Active Controller after a reload, the bootup standby will assume the active role
after reloading every unit in the stack, including itself.
• During a stack merge, the Active Controller with the highest priority will win the election and
reload every unit of the losing stack.
NOTE
Synchronization between the Active Controller, Standby Controller, and stack members will occur
whether or not hitless stacking is enabled.
When hitless stacking is enabled, the following behavior takes effect immediately:
• If a failover occurs, the stack will not reload.
• Manual switchover (CLI command stack switch-over) is allowed.
• If a priority change occurred while hitless stacking was disabled, and the configured priority
value requires a switchover, the system will start a 60-second timer before performing a
switchover. After the switchover, the highest priority standby will become the Active Controller.
• If there is no Active Controller after a reload, the bootup standby will assume the active role in
approximately 60 seconds without a reload.
• During a stack merge, the Active Controller with the larger number of units will win the election
and reload every unit of the losing stack. If two stacks have the same number of units, then the
priority, system up time, ID, then MAC address is compared. If two stacks have the same
number of units and the same priority, then the stack with the longest system up-time (by 30
seconds or more) will win the election. Otherwise, the smallest ID is compared next, followed
by MAC address. If the losing Active Controller has the highest priority, it will become a standby
after reloading and relearning the protocols. Finally, it will become the Active Controller after an
internal switchover.
NOTE
If the Active Controllers of two merging stacks have different hitless stacking settings (i.e.,
hitless stacking is enabled in one stack and disabled in the other), the default behavior (hitless
stacking disabled) will be used in the stack merge. After the merge, the winner will retain its
hitless stacking setting and runtime configuration for the merged stack.
You can use the show stack command to view whether or not hitless stacking is enabled. Refer to
“Displaying hitless stacking status” on page 174.