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Energy Efficiencies

by Hu Yoshida on Mar 5, 2012

Two events in 2011 are bringing greater focus on energy efficiencies.

First, the Fukushima disaster, which has decreased the use of nuclear power generation around the world, has resulted in increased costs for other sources of electrical energy.

Second is the record increase in carbon emissions, which is partly the result of the economic recovery in 2011 and the increased use of carbon fuels to replace nuclear power. The increase in carbon emissions and linkages to global warming are increasing the probability of carbon taxes. As a result, IT has become progressively more focused on energy efficiency and reducing carbon emissions.

In addition to increasing the efficient use of IT systems, the systems themselves must be redesigned to be energy efficient. Some of the recent improvements include:

Small Form Factor (SFF) Disk Drives

A 2.5 inch disk drive uses about half the power of a 3.5 inch disk drive. So moving from 2.5 inch drives to 3.5 inch drives provides a significant reduction in power. While the SFF drive may not hold as much capacity as a 3.5 in drive, it can be spun at a faster RPM and still consume less power. A common practice with 3.5 inch drives is short stroking, where data is written only to a portion of the tracks in order to reduce track seek time. This can be eliminated with SFF drives as well as with new capabilities, like page level tiering.

Solid-state Drives

Since solid-state drives are not mechanical, they consume less power and generate less heat than spinning disks—however, they are very expensive. This higher cost can be mitigated if they are used with automated page level tiering, where a small percent (less than 10%) combined with large capacity spinning disk will require less spindles of spinning disks to achieve the same or better performance than a single tier of high performance disks. Fewer spindles mean less power and cooling.

Front-to-Back Cooling

In the past, large enterprise systems were designed for density, with disk drives mounted in the front and back of the frames. This required a raised floor in order to suck cooling air from the plenum under the floor and exhaust the hot air out of the top of the frames; acting like a chimney. The fans were mounted on the top and were very powerful, so it sounded like a jet airplane. Those fans took a lot of power.

Today, large storage systems have adopted front-to-back cooling in a similar manner as modular storage systems. The advantage with front-to-back cooling is the ability to provide more efficiency by configuring frames back-to-back so that the cooling can be focused on the hot rows. This reduces the mixing of hot and cold air by containing the hot exhaust air in a specific area. Many data centers build enclosures around the hot rows to further isolate the hot air. Since our data center in Santa Clara is used for development and testing, we use the heavy plastic strip curtains that you see in cold storage facilities to contain the hot rows, while giving us ready access to the back of the storage frames.

Dense Drive Modules

When large enterprise storage vendors moved to front-to-back configurations, they shifted to larger frames in order to maintain their drive density. These frames are much larger than the 19 inch racks used with modular storage systems. They use a common disk drawer configuration with 15 (3.5 inch) to 24 (2.5 inch) drives in the front of the drawer and powerful N+1 fans in the back of the drawer, which have to suck the air from the front to the back.

The reason the disks are only mounted in the front is so they can be accessed for online service. They also had to cluster many of these frames together to deliver the same drive capacity as they had in older frames. One vendor has to cluster together 11 frames that are 30 inches wide in order to match the drive capacity of 6 VSP frames that are only 24 inches wide.

The reason we can pack more into fewer VSP frames is due to the design of a dense disk module, which can hold 80 x 3.5 inch drives or 128 x 2.5 inch drives in a 13inch high x 19 inch form factor. We also redesigned the cooling so that bifold fan doors in the front pull in the cold air, while the bifold fan doors in the back pulls out the hot air. This combination enables VSP to run the fans at a much lower revolution, which lowers power consumption.

If you stood next to VSP you could barely hear the fans spinning. The bifold fan doors also enable the drives to be serviced either from the front or the back without stopping the system. When we open one of the fan doors to service a drive behind it, the fans in the other doors will pick up speed to maintain the cooling. Another competitor of ours uses the same low power SFF drives that we use. However, since they did not redesign their drive drawers, they consume more power and floor space than VSP.

HDS: More Energy Efficient by Design

HDS is committed to ISO 140001 for improvement of energy efficiency. This begins in the product design phase to ensure that each generation is more energy efficient than the previous product. It also requires improvements in energy efficiency in the supply chain, manufacturing, distribution, maintenance, and end of life. Hitachi’s corporate goal is to reduce power consumption in the data center by 50% and reduce CO2 emissions by 330K tons over 5 years. You can be assured that the next generation of VSP will be even more energy efficient.

For other posts on maximizing storage and capacity efficiencies, check these out: http://blogs.hds.com/capacity-efficiency.php

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