Anyone looking at how flash SSDs have revolutionized mobile computing could be forgiven for thinking that all SSDs run cool and sip power. But they don't.
Flash technology isn't ideal for high performance apps. Each flash die has limited bandwidth. Writes are slow. Wear must be leveled. ECC is required. DRAM buffers smooth out data flows. Controllers run code to manage all the tricks required to make an EEPROM look like a disk, only faster.
So the number of chips and channels in high performance SSDs has risen to achieve high bandwidth and low latency. Which takes power and creates heat.
The price of performance
In a recent Usenix HotStorage '14 paper, Power, Energy and Thermal Considerations in SSD-Based I/O Acceleration, researchers Jie Zhang, Mustafa Shihab and Myoungsoo Jung of UT Dallas examined high-end SSDs, those with multiple channels, cores and flash chips. Fast, robust SSDs need all the help they can get.
They found that high-performance SSDs exhibit characteristics uncommon in lesser SSDs.
- High power. 2-7x the power, 282% higher for reads, up to 18w total.
- High temperatures. 150-210% higher than conventional SSDs, up to 182F.
- Performance throttling. At 180F the many-resource SSD throttles performance by 16%, equivalent to hitting the write cliff.
- Large write penalty. Writes at 64KB and above in aged devices caused the highest temperatures, likely due to extra garbage collection and wear leveling overhead.
Performance throttling was not limited to the high-end SSDs. A mid-range drive slowed down at 170F, probably due to thermally-induced malfunction as the drive had no autonomic power adjustment.
The Storage Bits take
I found these results a little hard to believe, so I looked at some high-end enterprise SSD specs. Sure enough, I found an Intel SSD spec'd at 25w - twice the power required for a 15,000 rpm enterprise disk - and higher than any the researchers tested.
Should enthusiasts be concerned? Maybe. The performance throttling from high temps of even mid-range SSDs could affect a game at its most intense. If your system gets sketchy at high temps, this could be a cause.
For enterprise users this is a reminder to check specs and understand power and cooling requirements for high density SSD installations. Free-cooled datacenters may also be at risk for SSD-induced slowdowns.
While not a huge problem for most people today, the insatiable demand for performance will move more of the market to these high-performance SSDs. The time to think about the impact is now.
Comments welcome, of course. Have you noticed any heat or power issues in your SSDs?