Businesses require a highly available campus network. Network switch power redundancy is a critical component of overall campus redundancy. Cisco StackPower is an innovative feature that aggregates all the available power in a stack of switches and manages it as one common power pool for the entire stack. This helps customers achieve more granular control over power use, resulting in savings that reduce the Total Cost of Ownership (TCO) of Cisco Catalyst switches.
This white paper focuses on the Cisco StackPower architecture and covers the following:
● Benefits of Cisco StackPower
● Technology overview
● Cisco StackPower operation
◦ StackPower budgeting
◦ Adding a new switch to a power stack
◦ Zero-footprint RPS
● Use cases of Cisco StackPower
● Intelligent power management
● Cisco StackPower topology
● Modes of operation
● Intelligent load shedding
● Best practices
Benefits of Cisco StackPower technology
The benefits of Cisco StackPower technology are immediately tangible, and so are the savings. Consider a stack of switches, with each switch requiring a slightly higher power budget for some extra Power over Ethernet (PoE) devices randomly scattered in the stack. Purchasing an extra second power supply for each switch that needs additional power would be inefficient and expensive. With the Cisco StackPower solution, a common pool of power is made available, and additional power can automatically be redirected to the appropriate switch based on the available power budget in the common power pool.
Cisco StackPower technology immediately produces savings by reducing the number of power supplies required per switch and the number of outlets required in the wiring closet. Additional savings accrue from minimizing energy waste due to inefficiency of power-supply operation at lower loads and reducing cooling requirements in the wiring closet. The technology also eliminates the need for external power shelves, thus freeing up additional space and power outlets in the wiring closet.
Cisco StackPower also allows the deployment of larger power pools by using a Cisco Expandable Power System 2200 (XPS 2200). This system allows for a star topology that shares power with up to eight switches. For details, see “Cisco StackPower Topology” section.
Cisco StackPower technology provides the following additional benefits:
● Abstracts the location of a power supply from its physical location in a stack of switches, allowing for better use of available power capacity
● Maximizes the efficiency of power supplies: Aggregated loads allow power supplies to operate at optimum efficiency, considerably reducing the waste of power over time
● Provides or complements the power required for PoE+ and Cisco Universal POE (Cisco UPOE®) to any port in a stack
● Enables a scalable PoE+ and Cisco UPOE infrastructure
● Offers a pay-as-you-grow architecture, similar to Cisco StackWise technology
● Offers improved reliability, availability, and efficiency with the XPS 2200 serving to up to eight switches
● Enables a “zero-footprint” Redundant Power System (RPS)
● Offers greater redundancy with the RPS:1+N vs. 1:N redundancy
● Allows offlining of power supplies when extra capacity is available in the system
● Lowers TCO by reducing the number of power supplies needed, the number of devices in the rack, the amount of heat in the wiring closet, and the number of AC outlets in the wiring closet
There are two commonly used power redundancy solutions for switches – full redundancy and partial redundancy. In full redundancy, every switch is attached to two power supplies, so that if one goes down, the other takes over. This scheme is also called 1:1 redundancy. In partial redundancy, there is one extra power supply for multiple switches. This is also called 1:N redundancy. Each has its drawbacks.
Fully redundant power solutions (1:1) are often underutilized because every switch has a backup power supply that is idle under normal conditions. However, partially redundant power solutions (1:N) take time to come online in the event of a power failure leading to an outage.
Cisco StackPower provides a revolutionary alternative to power redundancy for the Cisco access switches. It pools the available power supplies from all the switches and makes the pooled power available to all of them. The pooling of the power supplies is the most efficient way to distribute power to all the switches equally, because any switch can use the power from the pool, and if a power supply fails, excess power from the pool can be redistributed to the affected switch in no time.
Figure 2 shows the different types of power redundancy.
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