Use the copy running-config startup-config command from EXEC mode to save the new configuration to nonvolatile storage. Once you enter this command, the running and the startup copies of the configuration are identical.

This table lists various scenarios when module configurations are preserved or lost.

The switch has one or two supervisor modules of these types:

• Supervisor A (N9K-SUP-A) modules with four cores, 4 executable threads, 16 GB of memory, and 64 GB of SSD)

• Supervisor A+ (N9K-SUP-A+) with four cores, 8 executable threads, 1.8 GHz, 16 GB of memory, and 64 GB of SSD

• Supervisor B (N9K-SUP-B) with six cores, 12 executable threads, 2.2 GHz, 24 GB of memory, and 256 GB of SSD

• Supervisor B+ (N9K-SUP-B+) with six cores, 12 executable threads, 1.9 GHz, 32 GB of memory, and 256 GB of SSD

When a switch has two supervisors, one supervisor is automatically active while the other is in standby mode. If the active supervisor goes down or is disconnected for replacement, the standby supervisor automatically becomes active. If you replace one of two installed supervisor modules with another module, you can do so without interrupting operations. The supervisor that you are not replacing becomes the active supervisor and retains the kickstart configuration while you replace the other supervisor. If the switch has just one supervisor, you can install the new supervisor in the open supervisor slot during operations. Make that supervisor active after the installation.

Note

If there are two supervisors that are installed in the chassis, both must be the same type as shown in this table: Table 1. Active Supervisor Standby Supervisor Is Combination Allowed? Supervisor A Supervisor A Yes Supervisor B Supervisor B Yes Supervisor A+ Supervisor A+ Yes Supervisor B+ Supervisor B+ Yes

Supervisor modules are automatically powered up and started with the switch.

To understand the terms that are used for the supervisors, see this table.

Configure the power modes to either use (redundancy mode for when there is a power loss, or the combined power that is provided by the installed power supply units (no power redundancy):

n+1 redundancy mode

This mode allocates one power supply as a reserve power supply in case an available power supply fails. The remaining power supplies are allocated for available power. The reserve power supply must be at least as powerful as each power supply used for the available power. Use the ps-redundant command to activate this mode.

For example, if a switch requires 2.0 kW of available power and the switch has three power supplies that each output 3 kW, then one of the power supplies provides 3.0 kW of available power and one power supply provides 3.0 kW of reserve power, in case a power supply fails.

n+n redundancy mode

This mode insures load sharing, but the budget becomes half the total PSU capacity. Use a different power source for the active and reserve power sources, so that if the power source that is used for active power fails, the reserve power supply can provide power for the switch. To activate this mode, use the insrc-redundant command.

For example, if the switch requires 4.0 kW of power, the switch has four power supplies that each output 3 kW. If you have two power grids, you use both grid A and grid B to power four 3-kW power supplies that provide the available power for the switch.

Combined mode

This mode allocates the combined power of all power supplies to active power for switch operations. This mode does not allocate reserve power for power redundancy in case of power outages or power supply failures. This mode is not recommended for production.

The amounts of available and reserve power depend on the power redundancy mode that you specify. The amounts of available and reserve power also depends on the number of power supplies that are installed in the switch. For each redundancy mode, consider:

n+1 redundancy mode

The power supply that outputs the most power provides the reserve power so that it can take over for any other power supply that fails. All the other installed power supplies provide the available power. You activate this power mode by using the power redundancy-mode ps-redundant command.

For example, if the power requirement for a switch is 5.2 kW and the switch has two 3.0-kW power supplies outputting 3.0 kW each, consider these power planning scenarios:

• Scenario 1—No added power supplies

  One 3-kW power supply provides the reserve power and the other 3-kW power supply, also outputting 3.0 kW, provides the available power. The available power (3.0 kW) does not meet the switch requirements of 5.2 kW, so the switch powers up, except for some of its line cards.

• Scenario 2—Adding one 3-kW power supply

  One 3-kW power supply, which outputs 3.0 kW, provides the reserve power and the other two 3-kW power supplies, also outputting 3.0 kW each, provide enough power (6.0 kW) to meet the switch requirements (5.2 kW), so the entire switch powers up.

The table shows the results for each scenario.

Scenario	Power Requirement	Output (kW) for Power Supplies			Available Power	Reserve Power	Result
		1	2	3
1	5.2 kW	3.0 kW	3.0 kW	—	3.0 kW	3.0 kW	Available power is less than the power requirement for the switch. You cannot power the entire switch (some of the line cards will not power up).
2	5.2 kW	3.0 kW	3.0 kW	3.0 kW	6.0 kW	3.0 kW	Available power exceeds the power requirement for the switch, so the entire switch powers up.

For grid redundancy mode, the power supplies must be divided into two equal sets and installed as:

• Slots that are labeled as PS 1 to PS 4 must be connected to one grid (Grid A)

• Slots that are labeled as PS 5 to PS 8 must be connected to another grid (Grid B)

n+n redundancy mode

Half of the 3-kW power supplies are connected to one power source (grid) and the other half are connected to another power source. The available power is provided by one power source and the reserve power is provided by the other power source. If the power source that provides the available power fails, the switch uses the reserve power source to provide its required power. To activate this power mode, use the power redundancy-mode insrc_redundant command.

For example, if the power requirement for a switch is 5.2 kW and the switch has two power supplies that output 3 kW, consider these power planning scenarios:

• Scenario 1—No added power supplies

  The available power is 3.0 kW (output from one 3-kW power supply) and the reserve power is 3.0 kW (output from the other power supply). The available power (3.0 kW) does not meet the switch requirements (5.2 kW), so most of the modules power up, but some of the line cards will not power up.

• Scenario 2—Adding two 3-kW power supplies

  The available power is 6.0 kW (output from two 3-kW power supplies on grid A) and the reserve power is 6.0 kW (output from the other two power supplies on grid B). The available power (6.0 kW) exceeds the power requirement of the switch (5.2 kW), so the entire switch powers up.

The table shows the results for each scenario.

Scenario	Power Requirement	Output for Power Supplies				Available Power	Reserve Power	Result
		1	2	3	4
1	5.2 kW	3.0 kW	3.0 kW	—	—	3.0 kW	3.0 kW	Available power (3.0 kW) is less than the power requirement for the switch (5.2 kW)—switch powers up, but some of the line cards cannot power up.
2	5.2 kW	3.0 kW	3.0 kW	3.0 kW	3.0 kW	6.0 kW	6.0 kW	Available power (6.0 kW) exceeds the power requirement for the switch (5.2 kW)—the entire switch powers up.

Combined mode

The Total Power Capacity equals the combined output of all installed power supplies. There is no reserve power. To activate this mode, use the power redundancy-mode combined command. If the Total Power Allocated (budget) for a switch is 5.2 kW and the switch has one 3-kW power supply with 220-V input and 3.0-kW output, consider these power planning scenarios:

• Scenario 1—No added power supplies

  If you do not add a power supply unit, the available power (3.0 kW) is insufficient for the switch power requirement of 5.2 kW. The switch powers the supervisor modules, system controllers, fan trays, and at least one fabric module before powering as many of the fabric and line cards as the remaining available power can support (one or more fabric or line cards might not be powered).

• Scenario 2—Install an extra 3-kW power supply

  If you install an extra 3-kW power supply unit that can output 3.0 kW, the available power becomes 6.0 kW. The increased amount of available power exceeds the switch power requirement of 5.2 kW, so all the modules and fan trays in the switch power up.

The table shows the results for each scenario.

Scenario	Power Requirement	Power Supply 1 Output	Power Supply 2 Output	Available Power	Reserve Power	Result
1	5.2 kW	3.0 kW	—	3.0 kW	—	Available power is less than the power requirement for the switch. You cannot power the entire switch. Some of the line cards will not power up.
2	5.2 kW	3.0 kW	3.0 kW	6.0 kW	—	Available power exceeds the power requirement for the switch, so the entire switch powers up.

Fan trays provide airflow through the switch for cooling. Each fan tray contains multiple fans to provide redundancy. The switch can continue functioning in these situations:

• One or more fans fail within a fan tray—Even with multiple fan failures, the switch can continue functioning. When a fan fails within a tray, the functioning fans in the module increase their speed to compensate for the failed fans.

• The fan tray is removed for replacement—The fan tray is removed and replaced while the switch is operating without presenting an electrical hazard or damage to the switch. The switch can operate for three minutes without the fan tray that you are replacing, but if the switch air-inlet temperature is less than 86 degrees Fahrenheit (30 degrees Celsius), you have up to 72 hours to replace the fan tray. Because temperatures can change over time, we recommend that you replace the fan tray within three minutes.

• If you remove more than one fan tray at a time, the switch can operate up to three minutes before shutting down. To prevent a shutdown, remove only one fan tray at a time.

Note	When a fan fails or when you remove a fan tray, the remaining operating fans speed up to compensate for the loss of fans. This process can increase the noise that is made by the fan trays until you replace the missing fan tray or replace the defective fan tray.

Note	When replacing a failed fan tray in a running system, be sure to replace the fan tray promptly.

Tip	If one or more fans fail within a fan tray, the Fan Status LED turns red. A fan failure could lead to temperature alarms if not corrected immediately.

The software is continuously monitoring the fan status. In a fan failure, these actions occur:

• System messages are displayed.

• Call Home alerts are sent (if configured).

• SNMP notifications are sent (if configured).

To display the fan module statuses, see Displaying the Status for the Fan Trays.

Note	The fan trays fill slots FAN 1, FAN 2, and FAN 3 in the chassis.