Dell POWEREDGE M1000E - Manual (Page 146)

146 Managing a Switch Stack
If you move the master unit of stack to a different place in the network, make
sure you power down the whole stack before you redeploy the master unit so
that the stack members do not continue to use the MAC address of the
redeployed switch.
NSF Network Design Considerations
You can design your network to take maximum advantage of NSF. For
example, by distributing a LAG's member ports across multiple units, the
stack can quickly switch traffic from a port on a failed unit to a port on a
surviving unit. When a unit fails, the forwarding plane of surviving units
removes LAG members on the failed unit so that it only forwards traffic onto
LAG members that remain up. If a LAG is left with no active members, the
LAG goes down. To prevent a LAG from going down, configure LAGs with
members on multiple units within the stack, when possible. If a stack unit
fails, the system can continue to forward on the remaining members of the
stack.
If your switch stack performs VLAN routing, another way to take advantage of
NSF is to configure multiple "best paths" to the same destination on different
stack members. If a unit fails, the forwarding plane removes Equal Cost
Multipath (ECMP) next hops on the failed unit from all unicast forwarding
table entries. If the cleanup leaves a route without any next hops, the route is
deleted. The forwarding plane only selects ECMP next hops on surviving
units. For this reason, try to distribute links providing ECMP paths across
multiple stack units.
Why is Stacking Needed?
Stacking increases port count without requiring additional configuration. If
you have multiple PowerConnect switches, stacking them helps make
management of the switches easier because you configure the stack as a single
unit and do not need to configure individual switches.