Complementary Insults

In his recent Home Media Server Guide, Brian Won of Ars Technica briefly discusses the heat and space issues involved with packing lots of hard drives in to a personal server. Since these problems are handled nicely by cases such as the Cooler Master “Stacker” line and the Antec Nine Hundred, I started thinking about power consumption.

My question then became whether it would make sense from a financial perspective to pay extra for larger hard drives which you could then use less of, thus burning less power.

The drives I chose to compare are the 16MB cache models of Seagate’s Barracuda 7200.10 family. These are popular pieces of equipment with good reputations and a wide range of capacities from 250GB up to the 750GB behemoth and an anticipated 1TB model in the near future. Choosing this family also simplifies things dramatically because the manufacturer’s specification for power consumption is identical across the entire line, at 13 watts average. Based on my own experiments with the 250GB and 500GB models using my trusty Kill-A-Watt, these numbers are fairly accurate.

With the power consumption being the same across the entire line, it’s clear that using less hard drives means less power consumption. This then shifted my focus from whether there will be power savings to how long does it take for the power savings to overcome the initial investment.

After looking at the price per gigabyte, I eliminated the 250GB model from this comparison. This is because it costs more per gigabyte than the larger 320GB model, thus requiring both more drives and a greater initial investment to provide the same amount of space. There will never be a return on the investment when choosing the 250GB model, and thus I only recommend them if you must have storage space right now and can’t stretch for the extra $15 to upgrade to the 320GB model.

Now, we’re left with the 320GB, 400GB, 500GB, and 750GB models. Using the prices from Newegg on 2/1/2006, they are 3.37, 2.86, 2.5, and 2.21 GB per dollar respectively. I’m going to aim for a total capacity of 1.5TB when choosing the number of drives for each size. This is partially because it’s easy to hit close to with all four sizes and partially because it’s a reasonable size for a home server.

• 5x 320GB @ $95 ea. - $475 - 1.6TB
• 4x 400GB @ $140 ea. - $560 - 1.6TB
• 3x 500GB @ $200 ea. - $600 - 1.5TB
• 2x 750GB @ $340 ea. - $680 - 1.5TB

As you can see, I overshot a bit with the two smaller drives, but this is as close as they’d get without having to push these numbers way out of the home server range.

Here in Toledo, OH, I pay $0.137 per kilowatt-hour for electricity. Forget the math, but at 13 watts a piece this means that every hard drive I don’t have to power in a 24/7 server is a savings of $1.30 a month on my electric bill.

When we look at the up front prices, I’d be paying $85 extra up front to cut from 5 drives to 4 with no difference in capacity, $125 extra to cut out two drives (and losing 100GB in the process), and a whopping $205 to bring it down to only two running drives (also losing 100GB). That’s quite the investment for such minor anticipated power savings.

By now it’s probably clear that the break-even point based on power savings alone is a long way off. I went ahead and did the calculations, and here are my results: The shortest break-even time goes to the 500GB drives, which would have paid for themselves in a few days past four years. Second place goes to the 750GB drives, which break even about four and a half months after the 500GB models. The 400GB drives are the real losers here, taking nearly five and a half years to break even.  SEE BELOW

Given the up-front savings, not to mention the flexibility you gain by using more drives (RAID levels 5 and 6 for failure-resistance), it seems that the only logical choice is to keep buying whatever size offers the best GB/$ bang for the buck. The money saved up front can cover the extra electric costs for years to come, and given the current rate of technology development by the time the larger drives would reach their break-even point there will already be single drives on the market capable of storing this entire example array many times over.

Note: It has been brought to my attention that the 400GB drives are currently selling for $120 rather than $140. This cuts the total price for a 1.6TB array of them down to $480, only $5 more than the 5×320GB array. With the savings of $1.30 per month, this initial investment is now paid off in just shy of four months, not to mention the advantage that four-drive RAID controllers are far more common than six-drive models, especially on motherboards. With that in mind, it’s obvious that the 4×400 array makes more sense from both a financial and practical perspective.