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.'"
So if your not a laptop user and aren't currently benchmarking your drive how long will it last?
What is the power usage for real world office/ web browsing type use?
Impossible! Those results are obviously wrong!! Now go back and do the experiment. Keep doing different experiments until we get the desired results!
How dear you try and endanger my stock portfolio?!
I believe that much of the problem is that SSD's are still a new technology compared to rotating disks. Right now, engineers are more concerned with increasing capacity and just making the damn things work. These are much more important than efficiency. As time goes on and the technology gets more mature, efficiency will get more attention from engineers.
There is no "I disagree" mod for a reason. Flamebait, Troll, and Overrated are not substitutes.
I wish they would measure power usage under conditions that many notebook computer users actually use them in, which does not include running synthetic benchmarks on their computer 100% of the time it's running. Of course, if you keep the machine writing to the ssd constantly then it's not going to show power savings. But how many mobile users' usage patterns include constant reading from and writing to disk?
Now I'm even happier that I paid the extra $1300 for the SSD option in my MacBook Air.
That way it will run out of battery sooner, leaving me free to use a real computer.
I believe this comment from the article could explain some of this away.
'There could be a systematic error in the benchmarks shown: if the flash based "disks" are faster then the whole system CPU/MEM/Chipset would draw much more power with flash "disks" compared with conventional disks - just because the benchmarks could run more often in the same time.
Maybe one should compare something like playing video from disk where it is assured that the systems do precisely the same work?'
I would use one of these SSDs on a Desktop Computer or a Server, because in those two situations I am looking for performance, rather than portability that I would want in a laptop.
...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).
A 32" Philips HD ready CRT was around 100-110 W at the time I looked.
However, this is highly dependent on brand as well.
The thing is that Tom measured battery life with the hard drives constantly working.
He glosses over this with the following statement:
No, Tom, no one turns on their computer and simply waits for the battery to die. However, no one turns on their computer and has their hard drive constantly thrashing either.
Typical usage patterns include document editing, movie watching, music listening, etc, which involve very, very small amounts of hard drive access.
Use a better battery benchmark that leaves the hard drive idle most of the time, then come back and let us know how these drives fare.
Exactly... The thing about spinning platters is that it takes energy to start up _and_ keep it spinning. So obviously doing read/write 100% of the time would bias towards the conventional hard drives.
Hell, even read/write 10% of the time is too much for normal usage.
- These characters were randomly selected.
He makes the claim in the comments about the article that "well who just watches dvds? You have to keep the system busy and test that!" That's about as valid as setting the machine not to sleep and seeing how long it can idle there.
On an ultraportable especially, you aren't going to be churning the CPU with a benchmarking program. You won't be rendering animation frames. Mostly you'll be in a web browser or text processing program, waiting on the user to type something. With occasional spurts of OS and program start/stop. Good gosh it sounds like a MIX of tasks, rather than either extreme.
Slashdot Patriotism: We Support our Dupes!
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
Who thinks that maybe the overall bettery life would be more affected by the HEAT the laptop is putting out?
After all, most laptops I've ever dealt with or owned are compact little furnaces that have their hard drives, cpu, gpu, and everything else shoved in as little space as possible in order to make room for things like batteries and keyboards.....
thus if they remove a high heat generating device (even more so with a 7200rpm drive) wouldn't logic also assume that you reduce the amount of heat needing to be removed from the system?
thus the fans would run less often, and therefore drain less battery power.
not too mention the proposed savings by simply accomplishing tasks "faster" when it comes to disk access.
Because in general folks know how to do it (so you're not adding code complexity in most cases) -- and it seamlessly handles the odd folks who *do* eat all of their RAM in a workload and end up needing it. (And since the folks with big working sets relatively to current states also tend to be the folks paying more money... they do get listened to -- and these are the same folks that would require a perfect patch in 24 hours when they're unhappy, so you're much better off having a little planning pre-release than trying to crowbar this in post).
The thing to do is to make the virtual memory subsystem as efficient as possible about handling swap statistics just in case you need it so that the folks who really don't need it aren't aggressively impacted.
(Note: I am a virtual memory subsystem kernel engineer -- but not on Windows. I make no claim about how efficient or inefficient Windows is at doing this as a result. I would seriously expect that since they're designing the core kernel to operate from laptops up through Windows Server Whatever --
they have to accommodate cases beyond the 4Gb in your laptop should be enough to keep everything in core, though. )
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.
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.
i thought once I was found, but it was only a dream.
Seems unlikely to be all that power efficient to me... hauling around that huge bulk, and it sure didn't seem like Executor really made all that difference at the Battle of Endor from a capital ship perspective. (Probably because most turbolaser batteries seem to have really lousy guidance,
after all).
Oh... you meant those SSDs.... my bad.
All those chips for RAM require power too...
There are 4 boxes to use in the defense of liberty: soap, ballot, jury, ammo. Use in that order. Starting now.
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)
Used/tried a Quad G5 with 16 gig memory installed (mine has 4,5 GB).
Even on Leopard, that mainframe like monster will still create a 64MB swap file amusing us. I also saw 6 swapfiles has been created on my 4,5 GB RAM installed Tiger (OS X 10.4, doesn't have auto cleaning) after days of heavy load uptime.
Is it a strategic thing that OS kernel does? I remember reading some real weird stuff about Microsoft's tactic to swap the applications to disk even while they didn't have to but I can't find the file now. You seem to blame application developers which I can understand, does it have something to do with "pageins" and "faults" I see generally caused by badly written software?
In TFA, there is a graph on page 14 with power consumption measurements for the 5 drives tested.
The SanDisk SSD shows 1.0 watt active, 0.5 watt idle.
The Hitachi drive (magnetic) shows 3.2 watts active, 1.1 watts idle.
So even if the SanDisk drive spent 100% of its time in active mode and the Hitachi drive was always idle, the SanDisk drive should still provide longer runtime.
However, their runtime test (page 12) shows 7:03 runtime with Hitachi, 7:02 with the SanDisk.
All they have to say about this is:
Most of the power consumption measurements are in line with our results in Mobilemark 07. However, it has become clear that idle and maximum power do not provide the full picture when we talk about flash SSDs.
Well, something clearly is wrong here.
PJRC: Electronic Projects, 8051 Microcontroller Tools
The battery life of a flash-based iPod nano is basically identical to that of a HD-based iPod Classic. However - the battery in a Classic is much larger.
Obviously the use model for both devices is the same.
swapping is often done on a modern system in order to increase performance by increasing cache space. By swapping out applications that are almost never being used, like say, the quicktime tray or something, there is more ram available to cache program data for applications that you are using much more heavily.
ERROR: SIG NOT FOUND (A)bort, (R)etry, (F)ail?:
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).
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.
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.
Seems like many of the objections can be roughly translated as: "If Bob can toss 60 shovels of dirt a minute and Ray can only toss 50, and both walk out in the same field and each dig a ditch for an hour ... " Tom's site asked "which one consumed more calories?" Instead of "which one moved more dirt?" Either is a valid measurement to take. What I take away from the article is not "OMG they LIED" or even "OMG Tom LIED". Instead, it is that different SSD's have widely varying performance and power profiles that may or may not be better than more traditional solutions for any given task.
Even when I use something that hits my drive hard, it is far from continuous. In fact flash drives might have a chance to shine here as well as often one of the things that increases activity is the need for random access, which magnetic media isn't all that fast at. For example my harddrive works much harder than it has to when I'm doing audio mixdowns because it has to access multiple wave files at the same time. Most of the time is spent seeking from file to file, it takes comparatively little time to read the actual data needed. Flash, of course, has much faster random access. Thus for something like this it'd be loaded lighter, despite it being an "intense" use.