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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?
That's an excellent point. I was wondering if the metric should simply be different altogether.
What if we used MB/Watt or some such? The "disks" are supposed to be really good at some things (random reads) but don't hold too much advantage over others (long continuous reads). So how many WattHours does it take to load a continuous 50 GB file? How about a random 50 GB of data off a 128 GB disk? How does that compare to the same measurements with a standard magnetic disk? How does power consumption change between reading, writing, and mixed disk loads? Writing flash takes far more power than reading, doesn't it? Yet on a physical disk it's not that different in power requirements.
There are other things too. Operating systems still aren't designed around these things, they are designed for physical rotating disks. Do these things even have native controllers (designed for this purpose) yet, or are they still using modified rotating disk controllers like the first models used? As time goes on, better power saving features will show up, especially as the OS cooperates to tell this disk more information about what's going on. A well managed flash drive may be able to shut off large chunks of it's self and only wake up the bits that actually need reading/writing. That would help quite a bit, I'm sure.
PS: First time I've been to Tom's Hardware in 6 months to a year. Nice to see they found a way to make it uglier. Used to be a nice site. I especially like the "you must login to see the printer friendly version" trick.
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The problem is apparently that they're using lots of flash without power-saving (presumably cheaper than the other kind) and they're also not turning the currently-unused chips off. I can't speak for anyone else but I spend the vast majority of my time accessing a minority of the data on my hard disk. The technology already exists to reorder disk blocks based on usage and it could easily be adapted to reduce the number of flash chips which need to be activated in an SSD. Perhaps the time to first access is consider to be too large to implement this sort of thing without on-chip power-saving features, although I doubt it would be more than a few small fractions of a second.
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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. )
Somebody correct me if I'm wrong, but isn't it true that with HDDs, the system can auto-power them down when they're idle, but with SSDs, this can't be done as easily due to the nature of SSDs?
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Of course if the SSD is running under load the entire time it may actually run more often than a regular HD.
from real world benchmarks SSD's only gain is from random reads. writes, sequential reads, etc all prove that SSD's are only as good as a regular spinning disk if not far worse.
It is a trade off. both have advantages and disadvantages. Maybe in 5 more years SSD's will ultimately win but for now it can go either way.
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I think that as people request more power efficiency from their laptops, that we will be able to turn off logging, and any other unnecessary writing to the disk. I already boot up my laptop with the "noatime" option so that it doesn't cause an extra write to the disk every time I read a file. I think there's a lot we could do in order to cut down on the number of reads and writes we do. And since spin-up, and spin-down isn't a problem with SSD, we should definitely be trying to cut down on how much we use the drive.
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Call me some guy mystified by brands but after using Seagate cheap stuff (SATA) and SCSI for years and never seen these things actually fail (besides stupid filesystems), I wait for Seagate, Fujitsu, Hitachi like known brands to ship their SSD rather than being abused by some memory vendor who has no clue about the hard disks to buy some overpriced flash memory fantasy.
I also don't know the actual reliability of SSD too. What about journaling? Can it handle? A journal is still needed on SSD drive, what if kernel fails or OS filesystem layer goes nuts? A journal will be in same area of disk and will be written over and over millions of times.
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. It is like performance suicide if someone dares to put a very complex applications to "memory card" instead of phones built in memory.
They are trying to ship it before it is a technology fit to general use. Much like some video sites existed while everyone had to struggle with 56K modem.
My experience matches yours. I had a huge increase in battery life when I swapped out the HD in my Fujitsu Stylistic 2300 for a CF-IDE adapter w/ a 2GB (booting Windows 2000) and 4GB (data, swap space) CF cards in it.
Ran much cooler and was absolutely silent (no fan).
I was quite bummed when the system died.
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So what they are saying then is that this brand new technology is not as refined yet as the one that's been around for almost 30 years? Shocking!
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The technology already exists to reorder disk blocks based on usage and it could easily be adapted to reduce the number of flash chips which need to be activated in an SSD.
Uhhh... wouldn't that defeat the purpose of using wear leveling algorithms?
A more relevant technique would be to avoid turning on flash chips that do not have data you're accessing... but that is not as easy as it sounds when your data is (purposely) fragmented all over the place.
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Interesting, I didn't notice that. But one thing I did notice is that it didn't seem to take into account real world use, things such as at what point does the frequency of the extra power needed to spool up a HDD outweigh any power savings -- laptops are turned on and off a lot more than a desktop, and if the responsiveness is there, then people are going to put their computer to sleep more often to save power. None of that was taken into consideration. So technically, he may be right in some circumstances, but that might not be the way most people use them in the real world.
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.