Are SSDs Really More Power Efficient? 222
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.'"
Re:Good article.. BUT... (Score:2, Informative)
Tom = Patrick Schmid and Achim Roos
Re:Not so good benchmark (Score:5, Informative)
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.
Author = Clueless and Stupid (Score:5, Informative)
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.
Operating systems and their disk requirements (Score:2, Informative)
if your computer has enough RAM, it will access the drive quite infrequently, especially in many cases where power drain would be of concern, such as in those UMPCs.
...which tend to have reduced memory.
...and which ship with operating systems designed to run in reduced memory. Puppy Linux, for instance, hits the disk less than Windows XP on the same PC.
I really haven't found this to be true any more. My computer hits the disk pretty much all the time (for logging if nothing else)
Then increase the buffering on the logs. You can get away with it on a laptop because a laptop has a built-in 2-hour-plus UPS.
Re:Not so good benchmark (Score:5, Informative)
Re:Swap (Score:3, Informative)
well In linux and OS X you can actually disable swap. Windows however relies on it heavily, and with Vista under 4 gigs of ram you need swap space to store the entire OS.
Re:Good article.. BUT... (Score:5, Informative)
Old and inaccurate (Score:5, Informative)
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) [lenovoblogs.com]
[2]: SSD part 2 (March 08) [lenovoblogs.com]
Re:Still too new (Score:5, Informative)
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.
iPod counterexample (Score:3, Informative)
Obviously the use model for both devices is the same.
Re:Swap (Score:2, Informative)
Already debunked.... (Score:4, Informative)
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.
Take with grain of salt (Score:5, Informative)
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).
Valid Data -- Yet Invalid Conclusion (Score:2, Informative)
Intel rolled out a 100+ person pilot program of it's currently sampling SSD. Users noticed a giant increase in productivity for HD-limited activities and significant battery life increases (25%+).
While the data from the experiment is valid, it's not reflective of a client workload, where a user produces x spreadsheets and y emails in a typical day. Under the experiment performed, you're performing a poor-man's version of a enterprise workload, where the results are well known -- SSDs won't save power per server. However, since enterprise workloads are normally severly HD limited, this may lead to less servers required to do the same amount of work.
Re:Been there, seen that, got the t-shirt (Score:2, Informative)
...it's like LCD TVs, people also thought they consumed less power than conventional CRTs. Personally, I can warm my hands if I stick the palms up in front of my 32" LCD which chugs away at 152W when fully "lit" (powersave mode off).
Conservation of energy still applies here. It's not that LCD technology is necessarily less efficient (compare a scanning electron beam exciting phosphors to cold cathode fluorescent), it's that people have demanded (and gotten) much brighter screens, sometimes by a factor of 5-10 or more.
Obviously, if you're putting more light out of the screen, you're going to need to pull more energy out of the wall. There's no free lunch. If you care about saving power, turn down the brightness. Otherwise, don't sweat it.
(Incidentally, my old CRTs got quite hot, so there was plenty of wasted energy coming out of those, too.)
Re:Engineering is a trade-off (Score:4, Informative)
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.
I thought it was a good article (Score:2, Informative)
Re:Author = Clueless (Score:4, Informative)
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.
Re:Obviously that cannot be! (Score:2, Informative)
http://www.tomshardware.com/reviews/ssd-hdd-battery,1955-13.html [tomshardware.com]
Does that address your "miserable failure" conclusion, or am I missing something?
Re:Still too new (Score:3, Informative)
I maintain a flash device driver for an embedded system as part of my job, and I have to say you have an interesting mix of misconceptions and valid points.
First of all, I'm wondering what you think your phone's built in memory is. If it's not flash, I feel sorry for you if your battery dies. Second, the nature of flash memory makes it highly desirable to implement some form of journaling. To change one byte of a file, you have to erase a sector, then write it back with the one byte changed. It is much easier to just write it to a new location then invalidate the first copy. I don't make memory cards or SSDs, but it is my understanding that most memory cards do this behind the scenes, as the world's most popular OS is too dumb to handle flash memory correctly. The OS thinks it is writing to the same physical location, but behind the scenes it's changing on every write.
You made a good point about the millions of writes, though. I'd love an SSD for my root partition that hardly ever gets written to, but I think it would wear out too quickly for /home unless it was severely oversized, and I'd probably want to get a lot of RAM to use for /tmp instead. A lot of applications with autosave and disk caching would need to be reworked I think in order for ubiquitous flash drives to be feasible.
Re:More power but only while being hammered? (Score:3, Informative)
Yes, this is correct, flash has terrible power consumption while writing. TWO REASONS:
1. When you re-write any data word inside a block, you have to re-write the entire block. This can get power-intensive if you are doing random writes, and even sequential writes can eat a lot of energy (yeah, show me a flash controller that can detect, cache and optimize every sequential write perfectly).
2. Write voltages on flash are much higher than the read voltages, because the write voltage forces electrons through a thin insulator (quantum tunneling).
With an almost pure read-only role, like an mp3 player, flash will use much less power than a mechanical drive.