Posted by Jim Scherr on Tue, Dec 29, 2009
So you are looking for power distribution for your server racks. The basic PDUs are easy and inexpensive; the switched units are more than you need, but what about the Metered PDUs.
Metered rack PDUs have an LED display on the front of the unit that shows the amps being drawn by the circuit. That's kind of cool to have, but what do you do with it? The meter serves a number of purposes from the initial installation to adding additional equipment, but the key reason for the metered power distribution unit is to prevent a circuit overload that will take down your equipment.
As you initially load servers, network devices, or other equipment use the meter to ensure you are drawing less than the circuit maximum. For a 20A circuit the UL derated standard is 16A, and for a 30A circuit it is 24A. Remember the initial load is at idle so it will probably increase as your operations ramp up. Also, if you planned your layout based on device specs, realize the specs are written to maximums. The normal usage will probably be 30-40% less. If you operate from a co-location facility and you pay a monthly fee for each circuit, maximizing your circuits can save you a significant amount of money
For critical equipment, power redundancy is a widely used best practice. For power redundancy, a minimum of two power circuits are supplied to each cabinet, and multiple power supply equipment is used. The intention is that in the event of a lost circuit, due to a short or bad device power supply, the remaining circuit would be able to pick up the load and keep the equipment running. To work each circuit can be loaded no more than half the circuit maximum. Again, for a 20A circuit (derated to 16A), the maximum load would be 8A. Here the meter is extremely useful both in the initial build out and monitoring ongoing operations.
Many facilities teams also perform periodic audits of power consumption. I had a large TV network customer that audited the power draw of each rack twice a year. Before they moved to metered PDUs they spent three days measuring over 400 racks with a clamp meter. Using the metered PDUs they were able to complete the audit in half a day.
The metered power distribution units can also assist IT manager with planning out expansions. Not only do they give you an accurate depiction of what your current rack configurations consume, but they also help you identify racks that have capacity to add additional equipment. This can save you from needing to purchase additional infrastructure, like racks, UPSs, power circuits, and PDUs.
These are just a few of the uses for the local power LED meters. I am constantly impressed with the new and innovative ways our customers use our products. If you have any other uses you've found, please let us know.
Posted by Jim Scherr on Mon, Nov 09, 2009
Basic PDUs are simple and economical solutions for providing power distribution to your cabinet. Simple in terms of providing a single power input with multiple power outlets. Simple when compared to the features available with network connected power strips and switched PDUs, but a great deal of thought and design has gone into making them correctly.
Basic PDUs are best used in environments where the power draw is known, constant, stable and manned. They are very effective in cluster or supercomputing environments, where many identical non-critical devices are working together. They are also effective in small manned locations that have low density equipment racks.
Normally a computer rack is not a stagnant environment. Equipment is often being added, removed, or upgraded. People are often in the racks and things get banged around. For this reason, the steel enclosure, industrial grade components, and small form factor are ideal features in the rack environment. The steel enclosure prevents damage to the PDU when installing and removing other equipment. The smaller form factor also keeps the PDU out of the way during these equipment movements. The top quality components are designed to operate at peak spec levels for indefinite periods, withstand bumps and bangs, and last for years without maintenance.
Unlike your desktop power strip, a good basic power distribution unit will be rack mountable, either vertically in the back rack space or horizontally in one U of rack space. This secures the PDU to the rack and prevents the power strip from dangling by the connected power cords, sitting on equipment and overheating, or being accidentally kicked or dropped. A mounted PDU will conveniently present the outlets to the user and allow for clean rack organization.
One of the worst things that can happen, when working in server cabinets, is the inadvertent shutdown of equipment. More often than not this is caused by accidently unplugging a device or disconnecting the power strip. Good Basic PDUs avoid this two ways. First a good power distribution device shouldn't have an on/off switch. PDUs are designed to run constantly. An on/off switch merely provides a point of failure that can bring down the entire circuit. Secondly, cable retention clips, keep your outlet plugs securely connected. To remove a plug from a clipped outlet requires and conscious effort, and combined with cable labeling, accidental disconnects can be a thing of the past.
Sometimes the simplest tool is the most effective, but simple doesn't mean you need to skimp on quality or functionality. Depending on your application, a Basic Power Distribution Unit could be your best and most economical solution. You can find these Basic PDUs at
http://pdusdirect.com/power-distribution-units/basic/
Posted by Jim Scherr on Fri, Nov 06, 2009
The goal of this blog is to provide our customers with information about site changes, products, best practices, and frequently asked questions. We'd like to make this an informative site with a lot of customer input. So if you have any items you'd like to discuss let us know at support@pdusdirect.com and we will address them here.
We might also use this forum to answer, in greater detail, some the questions we receive from you the users. Our customer base is primarily IT professionals, who are exceptionally good at networks, but have not given power a great deal of thought. They often have a number of questions when looking for PDUs, and that's what we are here for.
More to come soon, so check back occasionally!