Dell PowerConnect J-8216 Software Guide for JUNOS version 10.3 - Page 376

Dell PowerConnect J-Series Ethernet Switch Complete Software Guide for Junos OS Because the purpose of power management is to ensure minimal system disruption when power is insufficient, slot power priority does not always determine which line cards receive power. In some cases, power management might provide power to a lower priority line card rather than a higher priority line card. For example: • If power is insufficient for a line card in a higher priority slot but is sufficient for a line card in a lower priority slot, the lower priority slot receives the power. For example, if an 8-port SFP+ line card requiring 450 W is in a higher priority slot than a 48-port SFP line card requiring 330 W, the 48-port SFP line card receives the power if there is more than 330 W but less than 450 W available. • In an operating switch that has insufficient power, power management does not power off operating line cards to provide power to a newly inserted line card or a line card that is brought online after being offline, even if the line card has a higher priority than the currently operating line cards. However, if you restart the switch, power management reruns the current power budget policy and powers line cards on or off based on their priority. As a result, line cards receive power strictly by priority order and previously operating line cards might no longer receive power. • If you change the assigned power priority of line cards when there is insufficient power for all the line cards, power management does not power down line cards that had been receiving power because they are now a lower priority. Power Supply Redundancy By default, power management in J-EX8200 switches is configured to manage the power supplies for N+1 redundancy, in which one power supply is held in reserve for backup if one of the other power supplies is removed or fails. You can configure power management to manage the power supplies for N+N redundancy. In N+N redundancy, power management holds N power supplies in reserve for backup. For example, if your switch has six power supplies and you configure N+N redundancy, power management makes three power supplies available for normal operating power and reserves three power supplies for redundancy (3+3). If you have an odd number of power supplies, power management allocates one more power supply to normal operating power than to redundant power. For example, if you have five power supplies, the N+N configuration is 3+2. Given the same number of power supplies, an N+N configuration usually provides less normal operating power than an N+1 configuration because the N+N configuration holds more power in reserve for backup. Table 43 on page 304 shows the effect on normal operating power in N+1 and N+N configurations. Table 43: Available Operating Power in N+1 and N+N Redundancy Configurations Number of Power Normal Operating Power in N+1 Normal Operating Power in Supplies at n W Each Configuration N+N Configuration 2 1 x (n W) 1 x (n W) 304