Planning Power Redundancy
The Intel-based Xserve has the option to provide power-supply redundancy. While this is a welcome improvement, not all systems have this capability. Additionally, if power supplies aren’t receiving power, it doesn’t really matter how redundant they are.
To combat this, systems can include Uninterruptible Power Supplies (UPSs). Essentially, a UPS is a large battery acting as a hot spare (online and ready to take over) to facility power. In larger setups, generators start when facility power fails. This way, power is restored from some source before UPS batteries are drained. Properly implementing a UPS requires some analysis. The following steps you through an overview of the planning process:
Step 1: Identify devices that require UPS backup
While not all devices require battery backup, more devices than just servers need UPS batteries for high availability. Be sure to include all devices in the chain of dependencies, including network switches, modems, external online storage such as Redundant Array of Independent Disks (RAID) units, and Fibre Channel switches.
Step 2: Calculate power consumption
For instructions on determining the total power consumption of electrical devices and how to size a UPS. A system, however, is a dynamic thing. Don’t forget to periodically revisit the load placed on the UPS devices supporting upgraded equipment that may draw more power than the previous piece, or in racks that are being added to.
Step 3: Determine the required run time
Estimate or measure the time you need a UPS to support all of its equipment after power fails. This includes the time to send notifications and start generators, or the time to gracefully shut down your servers and other devices.
Step 4: Identify the required battery capacity
Unless someone in the group has prior experience in determining the right battery capacity, you will need outside help. Most vendors will be happy to aid in the process. Alternatively, most vendor websites have run-time calculators to help size a UPS for your needs. For example, APC’s UPS selector can be found at http://apc.com/tools/ups_selector/. An alternate vendor, Liebert, tends toward larger installations, and will have a representative assist when necessary (http://www.liebert.com).
Step 5: Research and select UPS vendors and models
While you may already have a good idea of a preferred brand of UPS, manufacturers change products and capabilities all the time. Ensure that a particular brand supports Macintosh environments. (This shouldn’t make a difference, but nevertheless, some manufacturers still throw up their hands upon hearing “Macintosh.”) Also, check with any value-added resellers (VARs) that your company works with; they may have bundles and real-world experience with various models and interaction with Mac OS X.
Step 6: Verify electrical ratings and wiring in your facility
Larger UPS devices typically call for 30-amp circuits, and place their own load on an electrical system as they charge batteries and run tests. Have a licensed electrician evaluate the electrical plant where any UPS will be installed. Let UPS systems save you from problems rather than create them.
Step 7: Determine the UPS communication method
You must also determine how UPS communicates over the system, whether through Mac OS X or other systems such as Linux and Windows. Most UPS models contain the ability to signal status over an IP-based network or serial ports. The appropriate software is required to interpret these signals and shut down as appropriate. Mac OS X has built-in support for communicating with a UPS over a USB cable. If Mac OS X detects a supported UPS, you can use the Energy Saver Preference pane to determine shutdown aspects of the OS.
Mac OS X–compatible software is available from some UPS manufacturers. Additionally, open source software has sprung up to enable network-based shutdown of systems. For example, apcupsd, the APC UPS monitoring daemon, supports Mac OS X systems as well as Linux and Windows, allowing a common interface across multiple platforms (http://www.apcupsd.org/).
Step 8: Test the UPS
Have a test plan that simulates power outages. Most UPS devices can also perform self-tests and report on battery statistics. Be sure to include power systems in a test plan.