Does Power-Saving Technology Kill SSD Performance?

Outlook, Conclusion And Remaining Questions & Answers

We were amazed to see these results, as they come at a time when many tech publications are spending a lot of time analyzing the disadvantages of flash SSDs. Flash SSDs such as the X25-E (for servers) and the X25-M (for consumers) have tremendous performance potential—to pick the right wording. But you have to get the appropriate product for your particular applications: high-end SLC flash SSDs are great for I/O-intensive applications, while MLC flash drives provide more capacity at a lower price, but at the cost of decreased write performance and I/O throughput.

Both types of drive may be impaired by block-level fragmentation and/or changes of usage model at some point. It is still up to the user to use her or his SSD in the most efficient way, avoiding fragmentation and eschewing the use of file-system based defragmentation tools, which won’t do any good.

Conclusion: Power Saving Can Reduce SSD Performance

However, our findings are significant, as they can affect users who may not even know they are running an SSD with the brakes on. In short: really fast SSDs that can deliver 200 MB/s or even more of throughput become limited by CPU performance due to power saving mechanisms—or more precisely, they are bottlenecked by a limited availability of CPU time. This became obvious by switching the various power saving options on and off. We found that the sophisticated power saving mechanisms—such as the Active State Power Management for PCI Express, or the deeper C states that switch off entire functional units within the CPU at a transistor level—have a noticeable impact on the performance of our X25-E flash SSD. Obviously, the latency added by utilizing the more complex power saving features is significant enough to have to wait for the system to pick up data.

The conventional power saving techniques, such as Enhanced SpeedStep—which reduces clock speed and voltage during idle or low load periods—showed the least impact. This is also the case for C1E mode (enhanced halt). Thus, we recommend keeping both of these enabled, as they contribute to lowering CPU temperature while reducing power consumption. All of the sophisticated power saving mechanisms are questionable for fast, SSD-powered systems. We believe that it does not make sense to go for a hardcore flash SSD product, just to lose performance on the way due to sophisticated power saving features. Check your BIOS options should your SSD performance not be at the level you expect it.

Remaining Questions and Answers

There are several questions we did not answer within our evaluation, which we’ll briefly cover here:

Why did we use the Intel X25-E?

We used it because it’s the fastest flash SSD currently available. It allowed us to create sequential throughput that exceeds 200 MB/s.

Do the findings affect I/O performance as well?

Yes, but the impact is comparatively small.

Will the results be the same on other motherboards?

We quickly tried a third board, and saw the same results. Depending on the individual implementation of power saving options, and the processors used, the performance difference will vary. However, the same conclusion remains: a fast SSD requires a fast processor to unleash its full performance.

Do power saving options also affect hard drive performance?

No. The fastest hard drives available are still far from reaching 200 MB/s. We benchmarked two 15,000 RPM SAS drives, but could not see a difference as significant as was the case with the Intel X25-E flash SSD.