Slashdot Mirror
Are SSDs Really More Power Efficient?
Bakasama writes "Tom's Hardware compared the power performance of several available SSD cards with a Rotating HDD that was chosen specifically for its poor power efficiency.
The results seem to fly in the face of current wisdom.
'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.'"
Yeah, another post mentioned that a SSD's power consumption during load is higher than another magnetic disk on idle... here it is:
"The SanDisk SDD drive at LOAD requires 1.0 mW while Hitachi HDD requires 1.1 mW at IDLE"
Of course, benchmarks are always a better indicator. Also, to be clear, as mentioned in the article (which I'm sure nobody else read), the test was performed by repeatedly running a benchmark on the system until it ran out of battery, so the test with the SSD is likely to have run the test more often.
I have a 32GB SSD in my T61. My real life usage shows that I get between 30 and 45 more minutes of battery life out of my SSD-equipped notebook than on my other T61, which has a 160GB 7200rpm drive in it, when both of them are on the "medium" power saving setting in Windows.
-- I wanna decide who lives and who dies - Crow T. Robot, MST3K
Actually two out of four SSD's reviewed used MORE power when idle than the 7200rpm drive, that's just stupid. The Sandisk used about 60% less, so there's a reason to go with the name brand in this case, they do a heck of a lot more R&D than simply throwing some components together off the shelf.
There are 4 boxes to use in the defense of liberty: soap, ballot, jury, ammo. Use in that order. Starting now.
It's not that SSDs use less power when idle, it's that they can transition between idle and non-idle modes much more quickly. Spinning up a hard disk takes several seconds and uses more power than leaving it spinning. Turning an SSD on is just a matter of putting power into the flash chips. This means that you can turn of an SSD as soon as you stop writing, while a mechanical disk can only be powered down when it's not likely to be used for a few minutes or more (and, even then, degrades the user experience by making them wait for it to spin up again). If you are hitting the disk for a second once every ten seconds, then an SSD needs power for six seconds per minute, while a hard disk needs power for 60 seconds per minute. Looking at the disk activity graph on my laptop, this is about the usage pattern that I see most of the time.
I am TheRaven on Soylent News
The article states nothing new - there are two very interesting blogs from Lenovo which already stated the same in August 07 (!). To quote:
Solid state HDDs promise to save power compared to traditional hard disk technology. And they will. However today's generation of SSDs have no power savings benefit compared to traditional HDDs. The big reason is that current SSDs with a Serial ATA interface are actually Parallel ATA hard disk drives with a serial bridge chip. They don't offer support for low power interface states and the architecture has a potential for data-losing error conditions when recovering from a low power state like suspend or hibernate. In the future, there will be native SATA solutions which will solve many of these problems and will at the same time offer a real power savings benefit which should increase battery life.[1]
An updated quote from a newer blog:
Power Consumption - All SSDs are going to save you battery life on your notebook, but some will save you more than others. Again, the native SATA drives will give you better battery life.[2]
To summarise: old news and mostly outdated with very recent SSD drives.
[1]: SSD part 1 (Aug 07)
[2]: SSD part 2 (March 08)
I could never buy the "speed" claims of SSD not just because I use very fast SCSI stuff but I actually see the horrible performance of them in my smart phone, HD Camera.
Connect your very fast SCSI drive to your phone and see if it's still as fast.
c++;
The testing methodology was flawed to draw any conclusions. The problem is the CPU may have been more active due to less IOWait states. AS a resulte, the drive consumption may be lower, and the benchmark was not throttled to the platter disk performance. The benchmark might have run many more times during the test.
XML is like violence. If it doesn't solve the problem, use more.
The title "Some SSD devices are inefficient" just does not drive page clicks. So Tom sensationalizes some facts, omits others, runs questionable synthetic benches and Voila... Slashdot delivers the page hits.
Tom sometimes takes known "problems" and dramatizes them. After all, an objective view should not be allowed to stand in the way of revenue generation.
As others have pointed out.
1. The reason for inefficient drives was usually power hungry interface logic chips.
2. The newer drives are all better according to a Lenovo blog (thanks jlp2097)
And to top it off the numbers don't even add up (see PJRC's nice post above).
That's 2ms grey-to-grey (or worse...).
At best you're looking at 4ms (white-to-black) which is 250 Hz.
Black to white is actually generally faster than grey-to-grey, not slower. That's why the whole grey-to-grey benchmarks started showing up. Because screens that could go black-to-white in 4ms were easily available, but they still had grey-to-grey times of 32ms for some level transitions.
Further, most 'fast' screens use 'overdrive' which actually overshoots the target destination color (because larger transitions are faster than smaller ones), and then brings it back down to the target color. (leading to 'sparkle' when whatching movies etc because a pixel on a small transition from 'almost black' to 'just a little bit less almost black' shoots through medium-grey to get there.
At Apple (a few years ago), we would test typical portable battery life by scripting a set of tasks for the computer, both in OS X and in Windows. This way, we would be trying to simulate this common mix of tasks and obtain more realistic battery lifetimes (and comparison between similar Windows laptops and our own). Naturally, it wasn't always the case that our benchmarks were the ones put up on the web.
Stuff like this benchmark is really just an extreme corner case. As an engineer who relies on lots of hardware to help perform long and complex simulations, I know something about thrashing a system to death. And yet, I would never, ever, ever run such a continuous thrasher on my laptop (at least without plugging it into the wall). Their scenario seems (to me) as extremely unrealistic and may qualify as FUD.