The value perspective
Still with me? Congratulations, you've reached our famous value analysis, which adds capacity and pricing to the performance data we've explored over the preceding pages. We used Newegg prices to even the playing field for all the drives, and we didn't take mail-in rebates into account when performing our calculations.
Our value calculations require a single performance score, which makes things a little complicated. We've come up with an overall index that normalizes SSD performance against a common baseline provided by the Caviar Black. This index uses a subset of our performance data, including HD Tune's random 4K response times and average transfer rates, our used-state FileBench results, scores from all five DriveBench 1.0 workloads, mean DriveBench 2.0 service times plus the percentage above 100 ms, IOMeter transfer rates for each access pattern with eight outstanding I/O requests, the Windows 7 boot duration, and our load times in Portal 2 and Duke Nukem Forever.
Time constraints prevented us from using a slower baseline drive than our Caviar Black, which actually scored better than a few of the SSDs in a couple of DriveBench metrics. To prevent those scores from jacking with the overall results, we've fudged the numbers slightly to match our mechanical baseline. Calculating overall performance scores is an imperfect science, and I may have to dust off our old 4,200-RPM notebook drive to set a new baseline for future reviews.
We've been using a harmonic mean to generate our overall score for storage performance because it does a good job of handling normalized results that can vary by several orders of magnitude from one test to the next. After much reading on the subject and calculating numerous performance scores in previous storage reviews, we're convinced this is the best approach for our particular mix of tests.
In terms of raw performance, the SandForce-based Force SSDs scale up to higher capacity points better than the competition. The asynchronous and synchronous configs both enjoy big increases in overall performance when moving from 120 to 240GB. The other big winner is the Intel 320 Series, whose 300GB variant vaults the drive from last place to a smidgen ahead of the fastest Crucial m4. Meanwhile, the 510 Series offers the least incentive to add capacity.
So, what happens if we mash this overall performance score with cost and capacity? Magic! Or, rather, performance per dollar per gigabyte, which is divides each SSD's overall score by its cost per gigabyte. We'll express this value metric as a single score in a line graph before exploring the relationship between performance and cost-per-gigabyte in a scatter plot.
Taking the cost per gigabyte into account also factors in the range of capacities we're dealing with at each step on the ladder. The 240GB Force Series 3 occupies an enviable spot on our scatter plot, offering the lowest price per gigabyte and better performance than all but its GT stable mates. One could argue that the step up in performance to the GT is worth the extra cash.
If you're not keen on any of the SandForce SSDs, the Crucial m4's low cost per gigabyte at 256GB is rather intriguing. The high-capacity Intel drives are much pricier.
Although this analysis is helpful when evaluating SSDs on their own, what happens when we consider the cost of drives in the context of a complete system? To find out, we've divided our overall performance score by the sum of our test system's components (which total around $800 at Newegg before adding the SSDs).
Gobs of solid-state storage capacity ain't cheap, and considering the cost of a complete system shuffles our scatter plot. The 120-128GB drives are mostly lined up in the middle of the plot, while the others drift off into pricier territory to the right. Looking at the spread, the Force Series GT 120GB stands out as a pretty good deal. The Force GT 240GB is still the fastest drive overall, and its price premium looks justified as a result.
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