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Storage disc hardware guide: Part 1

Why is it that a disc drive can be bought for a couple hundred dollars yet I have to pay thousands of dollars to get a storage array?

Be careful about the items that you're comparing. The hard drives used in the consumer market are not the same devices that are used in enterprise storage arrays. Enterprise-class hard drives are designed to offer performance and reliability that are better than consumer-class drives -- this drives up the cost of enterprise drives and inflates the cost of enterprise storage arrays. For example, SATA enterprise or desktop disc drives that have gone through more exhaustive and time consuming testing and burn-in are also combined with dual-porting cards for availiabity -- adding to the cost of a drive.

 But the cost of an array goes far beyond the hard drives. Storage arrays also demand power supplies, cooling and controllers, many of which are redundant. Software design and testing also has to be included. And all of the design/engineering time that went into the array has to be recaptured over time. Array vendors also have to make a profit to stay in business and continue to invest in research and development, sales, marketing, etc.

From a practical standpoint, you could go off and buy the drives and other parts, write your own software/firmware and then stitch it all together to form your own storage array, but why would you want to unless you have a lot of free time and resources at your disposal?

Go back to the beginning of the Disc Hardware FAQ Guide.

How are drive power demands changing? What power-saving features should I be looking for when selecting drives for my storage array, and what is a sleepy disc drive?

Each new generation of drives offers better capacity and performance but is generally using less power -- both at spin up and during normal operation. It's important to avoid focusing on the individual drives. For example, small form factor drives are drawing less power but allow more drives to be packed into the same physical area. You may find that the total power demands of your new high-density array are greater, even though each individual drive may use considerably less power. Several large drive arrays already incorporate some form of drive power management at the system level, though the most interest is in managing power autonomously at the individual drive level, including different power modes. Also, look at the over all effectiveness of the drives and the storage controller to increase performance while reducing drive power consumption as opposed to simply looking at gigabytes of storage per unit of electrical power (watts).

Hybrid drives using substantial amounts of onboard RAM or flash memory to cache platter contents are particularly interesting in terms of power management. When the physical hard drive isn't actually needed, its contents have already been cached to onboard memory; the drive could operate at reduced revolutions per minute or spun down completely. Meanwhile, the drive's data is accessed from the onboard memory. When the needed data is not in memory, the drive is spun up and the platters are accessed.

Still, spin-up power remains an important issue. It's possible to spin down numerous drives and save substantial running power, but spinning up a large number of drives simultaneously can produce a significant surge in power demands. Frequent starts and stops may also have an adverse effect on long-term drive reliability. Consequently, a trend is to use multiple power modes on disc drives to vary performance and power consumption while prolonging disc drive use.

Go back to the beginning of the Disc Hardware FAQ Guide.


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This was first published in June 2007

 

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