Flash SSDs Don’t Improve Your Notebook Battery Runtime – they Reduce It
Flash-based solid state drives (SSDs) are considered to be the future of performance hard drives, and everyone seems to be jumping on the bandwagon. We are no exception, as we have been publishing many articles on flash-based SSDs during the last few months, emphasizing the performance gains and the potential power savings brought by flash memory. And there is nothing wrong with this, since SLC flash SSDs easily outperform conventional hard drives today (SLC = single level cell). However, we have discovered that the power savings aren’t there: in fact, battery runtimes actually decrease if you use a flash SSD.
Could Tom’s Hardware be Wrong?
No, our results are definitely correct. We’ve looked at almost a dozen different flash SSDs from seven vendors over the last few months, and measured acceptable or sometimes even disappointing power requirements with most flash SSDs. In an effort to determine the actual impact on notebook systems, we took four SSDs that we had available in our test lab, and ran a series of Mobilemark benchmark runs on a Dell Latitude D630 notebook. We found runtime differences of up to one hour (!) when using a flash SSD compared to a high-performance 7,200 RPM 2.5” notebook hard drive.
Will this Slow Down the Flash Memory Hype?
We don’t think so. Flash is cool, because it’s expensive, and because it does provide significant performance advantages (when SLC flash is used). But while our results are interesting for most users, they will be shocking to road warriors. You will see very clearly in the benchmark section that theory and real life are sometimes entirely different.
We still believe that flash-based drives will be the future for the performance segment, but they must not become a key component for energy-efficient notebooks and ultra-portables — where performance is secondary — as long as their average power consumption is higher than that of conventional 2.5” notebook hard drives. In fact, even a high-performance 7,200 RPM 2.5” drive provided better overall battery runtime than most of the flash SSDs we put through the Mobilemark test.
Memoright SSDs: The End of Hard Drives?
The HDD is Beaten
About six months ago, we reviewed Mtron’s Flash SSDs (Solid State Drives), which were the fastest hard drives for desktop PCs until the launch of Western Digital’s new VelociRaptor. Although the VelociRaptor is a conventional hard drive and therefore it cannot offer the extremely quick access times of transistor-based storage media, it is the best choice for most applications - and it offers almost 10 times the capacity at a fraction of the SSD drive’s cost. However, we found an even better drive for the real enthusiast: the Memoright SSD MR25.2-032S, which leaves any other conventional hard drive in the dust as far as performance goes.
It has become difficult to keep track of the developments in the Flash SSD storage market. Flash SSDs look and behave like mechanical hard drives, except that flash memory devices store data in the same way that your motherboard’s firmware device stores BIOS information. USB thumb drives use flash memory as well. Flash memory can offer good throughput and virtually zero access time, although write throughput and write access times can be clearly slower than the read values. While Flash memory doesn’t generate as much heat as a hard drive spinning at high revolution speeds and it’s also extremely robust, the media does not yet offer the capacities that PC hard drives are expected to have. A 2.5” notebook hard drive, for example, can store up to 500 GB and a 3.5” desktop drive’s capacity can total up to 1000 GB.
However, flash-based drives can come in 3.5”, 2.5”, 1.8” or even smaller sizes. Remember that memory cards such as CompactFlash, SD or memory sticks are all based on flash memory. Flash memory typically requires much less power than a conventional hard drive does, and it withstands shocks, such as when a laptop is dropped, better than conventional drives. Flash SSD storage capacities have reached 128 GB, although only 32-GB flash SSDs have moved into a price range that can be considered affordable.
But why do we make such a big deal about SSDs in the first place? There are two simple reasons: performance and energy efficiency. While traditional hard drives do not directly accelerate processing performance for CPU-intensive tasks or graphics performance, they have a very noticeable impact whenever the operating system, applications or application data are launched or terminated. Once software can be executed or data can be accessed from within the system’s main memory, the core components can show their potential. Until this is the case, data has to be loaded or stored from or to the hard drive, which is why we still have to wait seconds or even minutes for Windows or applications to start. Flash SSDs can significantly reduce user idle time by providing a good mix of quicker data access and good throughput. Lastly, flash memory devices can be more energy-efficient than conventional hard drives. However, an SSD’s energy power consumption depends on the number of flash components the device has for its capacity. Flash memory’s power consumption also can vary (MLC, SLC – see next page).
We already looked at various Flash SSD offerings from Samsung, Sandisk, Ridata and the Korean manufacturer Mtron, which has been offering the fastest flash SSD drives to date. Executives from SSD specialist DV Nation
ow Can Battery Runtime Be Shorter?
It’s important to answer this question, because it doesn’t seem like this should be the case. Most flash SSDs show power requirements in idle and when under load that are comparable to those of conventional 2.5” notebook hard drives. A typical 2.5” hard drive based on rotating magnetic platters usually requires between 0.5 W and 1.3 W when it runs idle, and from 2 W to around 4 W when it is under maximum load. Peak load occurs when the actuator has to move the heads back and forth on the disc surface due to lots of random accesses.
Let me emphasize a part of my last sentence: “when the actuator has to move the heads.” It’s important to understand that a conventional hard drive will only reach its maximum power requirement when you’re requesting random data that’s distributed all over the medium. In the case of sequential reading or writing, hard drives will not require much more than the idle power, as there is no energy-intensive acceleration and deceleration of the actuator.
Flash SSDs Only Know Two Power States
In contrast, flash SSDs only seem to know two states: active or idle. We don’t have specific information on this, but we received confirmation from two vendors that many flash devices don’t feature power saving mechanisms yet. On the one hand, the entire industry is looking to improve MLC flash to enable larger flash SSDs at sufficient performance levels. On the other hand, wear leveling algorithms are more important than power saving features, as durability may be an issue with SSD drives.
So while conventional hard drives may operate at relatively low power when little movement is required — such as during sequential read access — flash based drives do not. They will draw their maximum power level constantly when in use, and as a consequence, simply spend more total time drawing maximum power than conventional drives.
