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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 5x320GB 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.