I'm surprised that a search reveals not one mention of SanDisk's proposed industry standard drive speed metric of "vRPM", or virtual rotations per minute. When I first read this acronym back in January I immediately dismissed it as marketing fluff invented to make their upcoming SSD sound better. However, after finally reading SanDisk's
white note today on how to calculate vRPM, the measure appears to be very useful. The experts on here should read and critique it.
Quick summary: vRPM is a metric of a drive's IOPS that can be used to compare HDD IO performance to SSD IO performance as well as allow comparison between different SSDs' IO performance. This metric is limited to accounting for small (4k) random read/write performance. It therefore ignores all other measures of drive performance such as sequential reads/writes or IO performance at other block sizes. vRPM is calculated by a simple formula using data obtained from a benchmarking tool such as IOmeter (queue depth = 4).
Here are my simple thoughts. vRPM looks like a very useful way of comparing HDDs to SSDs and different models of SSDs to each other in terms of
small random IOPS which, as we know, have an enormous effect on drive performance. This seems significant to me because currently there is no attempt in the SSD industry to represent a drive's small random IOPs in the published specs. This makes comparing SSDs based on published specs futile. vRPM would rectify this. The lack of a figure like vRPM is the reason JMicron drives looked so great on paper but caused much confusion as an explanation of stuttering was sought. Since vRPM is solely a measure of small random IOPS it does not attempt to represent
bandwidth whatsoever. That's just fine - the only spec given by SSD manufacturers right now is precisely that (max sequential bandwidth). Adding a published vRPM spec to this would allow the average joe to compare apples to apples (SSD to SSD) as well as apples to oranges (SSD to HDD).
After reading the white note, I wonder if SanDisk devised vRPM partly to highlight how much better their upcoming G3 drive is than the previous JMicron drives (the data further below highlights this well). If in fact SanDisk can market the vRPM spec then it is all but certain that the SanDisk G3, with an identical pricepoint to the JMicron drives, will be the demise of JMicron.
With that said, it appears that SanDisk made some faulty predictions on the state of the SSD market in 2009. I think they were anticipating releasing their G3 SSD with only JMicron drives to compete with at the same pricepoint. They probably didn't plan on the Intel's price dropping so much (which takes away the enormous price advantage that they would have had) nor is it likely that they anticipated the entrance of the Indilix drives appearing at a comparable pricepoint yet significantly higher level of performance. These assumptions are supported when calculating vRPM values for all of these drives. Although the G3 is clearly better than the JMicron products, it is far behind the Vertex and not even comparable to the Intel. The price differential is too small between the G3 and the Vertex to choose the G3 based on price alone - and this doesn't account for the inevitable decline in the Vertex's price before the G3 will be released in "mid 2009."
Based on my calculations (using IOmeter data from my own solid,
Anand's article, and
Sandisk's website, here's how things stack up:
Code:
Drive Size vRPM Price
OCZ Solid 60 600 $160
7ms seek HDD 7,200
[COLOR="Red"][B][U][size='3']Sandisk G3 60 40,000 $149[/SIZE][/U][/B][/COLOR]
OCZ Vertex 60 73,000 $210
Intel X-25M 80 414,000 $363
What are your thoughts on using the vRPM metric as a matter of course when benchmarking SSDs?
Should we place pressure on SSD manufacturers to use and publish this spec?
Problems? See this thread at archive.org.
