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| About this blog: Computers hate me. They really do. Every time I try to do something unusual like add new hardware, something is guaranteed to go wrong. I decided to start writing about my constant problems so that someone else might benefit from my experiences - or at least laugh at them! |
| 04 February 2008, 11:30pm |
Purchase price per gig is easy to work out, but what about the running costs of the drives over their lifetime? I decided to do some quick back of the envelope calculations, based on the following assumptions:
1) Drives consume an average of 10 watts of power
2) Average cost per kilowatt hour is 15c
3) Average power supply efficiency is 80%, that is, a drive consuming 10 watts of DC will be drawing 12.5 watts "at the point"
Therefore the average cost per year to run a drive is 10W x 24 hours x 365 days x (1 / 0.80 efficiency) / 1000 x $0.15 = $16.42 per year.
Using a current price list from MSY Computers (in Australia) for Western Digital brand drives we come up with...
| Array size | Physical configuration | Purchase cost of drive(s) | Running costs per year | Effective running costs per gig
(3 years lifetime) |
|---|
| 1000GB | 1 x 1000GB | $289 (28.9c/gig) | $16.42 | 33.8c/gig | | 1000GB | 2 x 500GB | $258 (25.8c/gig) | $32.84 | 35.7c/gig | | 1200GB | 3 x 400GB | $345 (28.8c/gig) | $49.26 | 41.1c/gig | | 960GB | 3 x 320GB | $279 (29.1c/gig) | $49.26 | 44.5c/gig | | 1000GB | 4 x 250GB | $328 (32.8c/gig) | $65.68 | 52.5c/gig | | 2000GB | 2 x 1000GB | $578 (28.9c/gig) | $32.84 | 33.8c/gig | | 2250GB | 3 x 750GB | $588 (26.1c/gig) | $49.26 | 32.7c/gig | | 2000GB | 4 x 500GB | $516 (25.8c/gig) | $65.68 | 35.7c/gig | | 3000GB | 3 x 1000GB | $867 (28.9c/gig) | $49.26 | 33.8c/gig | | 3000GB | 4 x 750GB | $784 (26.1c/gig) | $65.68 | 32.7c/gig |
This scenario suggests that even though the 500GB drive has the best price per gig at purchase, the 750GB drive beats it in the effective lifetime per gig cost.
The 1000GB drives, although a little more expensive to purchase, bring the effective running cost down because you need fewer of them. They could also save you money in the long run due to taking up less physical space and controller ports, and generating less heat.
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