Lenovo Flex System Fabric CN4093 Application Manual page 206

However, for purposes of future Backup selection, reconfigured Masters retain
their identity as configured Masters, even though they otherwise act as Members.
In case the configured Master goes down and the Backup takes over as the new
Master, these reconfigured Masters become the new Backup. When the original
configured Master of the stack boots up again, it acts as a Member. This is one way
to have multiple backups in a stack.
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CN4093 Application Guide for N/OS 8.2