The elephant in the room
We'll be leaning on scatter plots when assessing value on the performance side of things, but that's not necessary to convey a simple truth: SSDs have a much higher cost per gigabyte than their mechanical brethren. In some cases, the difference is several orders of magnitude.
Yeah, there's just no touching mechanical drives if you're looking for cost-efficient storage capacity. But then there's nothing that says you have to house all your data on a single drive. For desktop PCs, we think the combination of a relatively low-capacity SSD, used as an OS and applications drive, and a high-capacity mechanical drive is the best approach. The minimum size of that system drive will depend on just how many applications you intend to keep on the SSD. By applications, I mainly mean games, which tend to have a gluttonous appetite for gigabytes.
As you can see, some SSDs have a more attractive cost per gigabyte than others. The Kingston SSDNow V+ leads the SSD pack, trailed closely by the X25-M, RealSSD, and SiliconEdge. Just behind those is the Nova V128, which is followed by Intel's budget X25-V and the Force F120.
SandForce-based drives with the higher 28% overprovisioning percentage are the worst values of the lot, costing at least fifty cents more per gigabyte than our lead group of SSDs. The F100 is particularly expensive, or at least it was when the drive was still selling online. The F100 has since gone out of stock, and Corsair may not bring it back given higher demand for the F120.
We have some RAID results for the X25-V that have been included in the mix, but that's the only SSD array we've tested on our new rigs. Since we used the RAID controller built into our motherboard's core-logic chipset, there's no additional cost associated with the array outside of the second drive. With RAID 0, the cost per gigabyte remains unchanged as drives are added to the array. Keep in mind that you can pair any of these SSDs in their own RAID array. Doing so will cost you TRIM and thus impact write peformance. As far as we know, TRIM isn't currently supported by any RAID controllers.
A question of value
Just how do we represent value? It all starts with an ancient 4,200-RPM notebook hard drive that's old enough to bear the IBM name. This geriatric 30GB Travelstar took its sweet time trudging through our benchmark suite, but it gives us a nice performance baseline against which to judge our contenders. Each drive's score in a given benchmark is converted to a percentage using the Travelstar as the baseline. We can then quantify performance per dollar, which should give us a very basic representation of value. This calculation blunts the impact of a drive's total cost, so it won't penalize higher-capacity SSDs for having a higher asking price, nor will it reward low-capacity models just for being cheaper than everything else.
Performance per dollar figures are easy to line up with bar graphs. Our scatter plots take a slightly different look at the same data. Instead of calculating a performance-per-dollar score, we simply map price on the X axis and the performance percentage on the Y axis, like so:
In theory, the sweetest spot is in the top left corner, which denotes the highest performance at the lowest cost. The worst place to be is the exact oppositethe bottom right-hand corner.
Most of the drives will likely fall between those two extremes, although mixing mechanical and solid-state offerings with vastly different access times could make things a little more interesting. Or a complete mess. Either way, the scatter plots will reveal the most noteworthy intersections of performance and price. The performance-per-dollar bar graphs are meant to complement to these scatter plots; we believe the scatter plots paint a richer picture of the value vista.
There are far too many components to our exhaustive suite of storage benchmarks to include every test, so we've whittled things down to the most relevant ones. We've settled on a mix of targeted and real-world performance tests that covers sequential transfers, highly randomized access, and usage patterns that combine both elements.
Honestly, I hate leaving performance data on the table. Some level of simplification is necessary for these sorts of value comparisons, though. You can always refer back to individual reviews for a more detailed analysis of the drives we're considering today. Those reviews also take value into consideration, although in a more general sense within the context of the drives' features and differences, rather than relying on quantitative performance-per-dollar measures and exotic scatter plots. This value comparison isn't meant to replace our in-depth reviews, but to provide a different look at the data we've collected.
Boiling value down to a couple of performance-per-dollar calculations has its share of problems. There are other factors that can affect a drive's perceived worth, such as warranty coverage and end-user support. SSDs are usually a little short on differentiating features, but SandForce drives do have on-the-fly encryption built in, and their lower write-amplification factor should ensure greater longevity than contemporary rivals. These are the sorts of things that our SSD reviews will cover in greater detail.
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