### Economics of PC Storage part 2 - Hard Disks

I mentioned on the OpenSolaris site that commercial NAS devices charge between \$1.60 to \$3.00 per GigaByte without redundancy. That is 0.33 to 0.62 GigaBytes per dollar. From two web sites I got prices in January 2006 for 30 hard drives.

A more interesting way to measure Hard Disk value is GigaBytes per Dollar

Assuming that the GB per \$ performance of hard drives can be represented as a quadratic we get
the red dotted line.

lm(formula = Size/Price ~ Size + I(Size\^2), data = mytable)

Residuals:
Min       1Q   Median       3Q      Max
-0.36294 -0.14051  0.02323  0.13648  0.38674

Coefficients:
Estimate Std. Error t value Pr(>|t|)
(Intercept)  6.514e-01  1.517e-01   4.295 0.000202 \*\*\*
Size         1.173e-02  1.169e-03  10.030 1.33e-10 \*\*\*
I(Size\^2)   -2.052e-05  2.030e-06 -10.107 1.13e-10 \*\*\*
---
Signif. codes:  0 '\*\*\*' 0.001 '\*\*' 0.01 '\*' 0.05 '.' 0.1 ' ' 1

Residual standard error: 0.1907 on 27 degrees of freedom
Multiple R-Squared: 0.7923,     Adjusted R-squared: 0.7769
F-statistic:  51.5 on 2 and 27 DF,  p-value: 6.093e-10

Solving the quadratic we get the best price performing hard drive would  be 286GB, sadly nobody makes such a drive but by eyeballing the graph the sweet spot is between 250GB to 320GB with a price performance above 2GB per dollar. Giving us a reasonable margin to build our OpenSolaris Appliance and still beat the comercial products 0.33 to 0.62 GigaBytes per dollar.

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rmd

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