To Save Energy, Spinning Down Hard Disk Drives Is Not Without Challenges

Here is an interesting IDC article written by Benjamin Woo, IDC VP of Enterprise Storage

Power and cooling, high energy costs, and the fact that more ‘old’ data is being kept on disk (supplementing tape) have given rise to strategies to manage the power necessary to spin hard disk drives. One of these strategies is to spin down idle HDDs that have not been accessed for a defined amount of time. Spin down strategies are viable, but they are not without challenges. Focusing primarily on enterprise storage, it is difficult to see spin down implemented en masse. Granted, some storage vendors and end users have storage architectures leveraging spin-down technology, but the use scenarios are limited to lower tiers of data storage, and only specific applications within those tiers.

The use of high capacity drives enables just a basic 4+1 RAID set using 500GB SATA drives to provide a 2TB LUN. Two terabytes is still quite a bit of storage for any given storage environment. If you virtualize this LUN into smaller volumes, then these volumes are likely to be mounted by different servers. As the number of servers increases, so too does the probability that the disk drives will be accessed. If this is a single LUN that is accessed very infrequently (the perfect application for spin-down technology), then the question that begs to be asked is "Why is the data being stored on disk media as opposed to lower cost tape media?" As one might suspect from this example, there is a danger for spin-down (so far) to be anything more than a way for storage system vendors to provide a check in the "Green IT" box.

Recently, however, this challenging view for spin-down technology changed at the recent EMC Innovation Day. In an operation akin to the legendary HP skunk works of yesteryear, an EMC engineer developed some software during his spare time, researched its viability, and a little over a year later, EMC (http://www.intel.com/pressroom/archive/releases/20071106corp.htm) Lifeline OEM software was born. The software itself can be used on any industry standard hardware, and essentially acts as a file, print, and backup server with built-in hardware RAID and an easy to use and understand GUI. One of the unique features of the software solution (which is targeted at networked home consumers, professional users, and small businesses) is the incorporation of spin-down technology.

Spin-down is a common feature used in laptop PCs (and sometimes desktop PCs) to conserve battery life and power and to reduce noise. In the data center, it is normally found only in enterprise class storage systems. However, EMC posited that spin-down has a great application in small businesses and in the home. Its premise, good and logical in my opinion, is that the duty load of these consumers and SMBs is not 24×7. Instead, the workload is much less. For example, a small business may be using the server only during business hours 5 days a week, and in the case of the home user, a centralized media server for the family may typically be used after the kids come home from school and on the weekends. These usage scenarios leave a significant amount of time in which the server, which is likely to be powered on constantly, can benefit from the power efficiency of spin-down technology.

The EMC engineer responsible for the Lifeline product should be commended for taking a very practical approach to the use of innovative technologies. In the end, outside of niche high-end use cases, I expect spin-down is viable and has a role in certain enterprise applications, but its mass appeal will come from the lower end of the storage market spectrum.

IDC