I was talking to a storage expert the other day and he mentioned a customer that I have worked with has chosen to go all SSD in its data center. I would assume the logic is SSDs are the most efficient solution and given their purchasing power they can get prices that few others can get, therefore the cost differential vs. HDD can become a non-issue. I heard this and think I know some of the people behind this and I questioned their assumptions to use SSDs as storage solution that eliminates HDD.
Digital Ocean has a lot of hype with their all SSDs environment and the idea that SSDs are the future can be a “false positive."
Doing a bit of research I found StorageMojo recently posted on SSDs - hot, hungry and slow.
High performance SSDs: hot, hungry & sometimes slow
Anyone looking at how flash SSDs have revolutionized power constrained mobile computing could be forgiven for thinking that all SSDs are power-efficient. But they’re not.
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 examine what they call “many-resource” SSDs, those with multiple channels, cores and flash chips.
The price of performance
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.
Bottom line here are some insights.
The many-resource SSD exhibits several characteristics not usually associated with SSDs.
- High temperatures. 150-210% higher than conventional SSDs, up to 182F.
- High power. 2-7x the power, 282% higher for reads, up to 18w total.
- 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, presumably due to extra overhead for garbage collection and wear leveling.
And here is the kicker, a SSD can consume 2X the power of a HDD.
The StorageMojo take
This appears to be the first in-depth analysis of the power, temperature and performance of a modern high-end SSD. The news should be cautionary for system architects.
For example, one new datacenter PCIe SSD is spec’d at 25w – higher than the paper found on slightly older drives. That’s twice what a 15k Seagate requires.
The paper StorageMojo refers to is here.
This paper closes saying many-resource SSDs are 4-5X more power intense than conventional SSD and HDD.
In this paper, our empirical analysis reveal that dynamic power consumption of many-resource SSDs are respectively 5x and 4x worse than conventional SSD and HDD. Many-resource SSDs generate 58% higher operating tem- perature, which can introduce SSD overheating prob- lem and power throttling issues. Based on our analysis, HW/SW optimization studies are required to improve en- ergy efficiency of modern SSDs in many user scenarios.