Cisco StackWise is a technology offered by Cisco Systems that allows for up to nine Catalyst switch 3750 series switches to operate as though they were one switch. This allows for greater resiliency, and performance.
With a dual redundant loop back plane connection at either 32-Gbit/s or 64-Gbit/s depending on the 3750 model.
One switch from the stack will act as the master switch. The master switch will maintain the stack and allow you to configure and monitor the whole stack as though one via a single console.
If one switch fails the remaining switches will continue to operate by looping back any information that would normally traverse the failed switch, effectively bypassing it. If the master switch fails, the next switch in the stack will automatically take over as master. This feature means greater redundancy, as one switch's failure will not bring about a failure of the entire stack.
As each switch contains the entire configuration for the stack one of the benefits of this technology is the ability to replace a down switch (any including master) with a new un-programmed switch. The stack will configure the new switch on the fly and allow for minimal downtime
StackWise effectively replaced the GigaStack found on lower-price models such as Catalyst 35xx and 29xx series.
Recently, there is a new variation of the technology, known as Cisco Stackwise Plus, offering 64Gbit/s nonblocking switching fabric speed.
Read more about this topic: Cisco Catalyst