Revisiting the Five-Minute Rule 153
In 1987, a study published by Jim Gray and Gianfranco Putzolu evaluated the trade-offs between holding data in memory and storing it on a disk. Known widely as the "five-minute rule," their research was updated and expanded 10 years later. Now, as jamie points out, Communications of the ACM is running an article by Goetz Graefe with another decennial update, evaluating the rule using hardware and software typical of 2007, with an eye toward how flash memory will affect the situation. An excerpt from Graefe's conclusion:
"The 20-year-old five-minute rule for RAM and disks still holds, but for ever-larger disk pages. Moreover, it should be augmented by two new five-minute rules: one for small pages moving between RAM and flash memory and one for large pages moving between flash memory and traditional disks. For small pages moving between RAM and disk, Gray and Putzolu were amazingly accurate in predicting a five-hour break-even point two decades into the future. Research into flash memory and its place in system architectures is urgent and important. Within a few years, flash memory will be used to fill the gap between traditional RAM and traditional disk drives in many operating systems, file systems, and database systems."
Flash memory? (Score:2, Insightful)
I couldn't quite figure out if the article willfully ignored the advent of SSDs or was written before they were available and not updated to include them (but it appears the article was updated to include other current technology).
Given the fact that SSDs are likely going to replace rotational media for most applications in the future, it makes this article basically meaningless, at least insofar as the fact that flash memory and the disk are/will be synonymous. As the article is basically predicated around the entire fact that flash memory will change the 5 minute rule to a degree, it invalidates the entire article.
To be relevant, the article really needs to include the current state of SSDs and a likely projection (10 year) of where the state of the art in SSDs.
I do, however, suspect we may see a shift from drives all together at some point (perhaps more than 10 years, but perhaps not) and the computer will just have persistent storage for everything in MRAM or some other technology that obliterates the line between RAM (for speed) and drives (for storage) - it's just one big pool that's hyper fast and persistent.
So really, I don't think this article has held up in even the intervening two years since 2007, and it certainly won't hold up for another 10 years.
What article? (Score:3, Insightful)
The article I read spent a good deal of time talking about flash memory. What article are YOU referring to?
Re:What article? (Score:5, Insightful)
The article I read spent a good deal of time talking about flash memory. What article are YOU referring to?
The article treats flash as something you place in between hard drives and memory. This turned out not to happen (with a few exceptions). SSD's simply replace hard drives. Hybrid systems are rare, and it doesn't look like they will become more common -- either you can live with the slowness of hard drives, or you can't. The mainstream will switch to SSD's for everything except backup applications.
There are some hybrid SAN's, but they're damn expensive. At that price they have a hard time competing with simpler pure-flash SAN's.
External hard drives == memory hierarchy (Score:3, Insightful)
This article indicates that Flash Memory (AKA SSDs) are only going to be an intermediary between rotational media and RAM.
If your handheld device or subnotebook PC has only an internal SSD and no internal hard drive, then you will store any data that doesn't fit on your SSD on a hard drive plugged into a Hi-Speed USB port, copying it to the SSD when it is needed. For example, you'd keep the video footage that you are editing on the SSD and other projects on the hard drive. That sounds to me like a memory hierarchy, albeit one that occasionally requires manual intervention to connect the (offline) long-term mass storage to the machine.
Re:What article? (Score:2, Insightful)
tOM
Re:Flash memory? (Score:2, Insightful)
SSDs are not likely to replace traditional hard drives any time soon, if ever. The cost differential is simply too high. While it is true that SSDs can effectively replace HDs on systems which do not require large amounts of storage (say, 64G-256G), the fact of the matter is that a 256G SSD is still three times as expensive as a 2TB hard drive. That is a 24:1 cost factor.
At the same time SSDs are becoming capable of replacing systems which do not have large storage requirements, HDs are becoming far more capable in systems which DO have large storage requirements, and driven by high resolution digital camera and video media consumer trends are clearly heading towards the larger storage requirement end of the spectrum.
-Matt
Re:Not to be confused with (Score:4, Insightful)
Re:Not to be confused with (Score:3, Insightful)
Well the confusion is, unlike your dirt-floor huts full of your own feces, in real countries like America we have clean tile floors with miraculous inventions we call "mops".
Re:Flash memory? (Score:3, Insightful)
Depends what segment you're talking about. There isn't one market for HDD's, there are many. In both the enterprise archival and consumer mass storage segments, drives are sold pretty much $/TB. In that segment, you won't see significant penetration for 4-6 years. In other segments, sooner. I agree with you: I want a flash SSD for my laptop currently; it just hasn't quite yet reached the right price point. It will soon. And you're right: it's not $/GB that will be the deciding factor there.
There's also no reason to assume one way or the other. For example, I expect to put BOTH flash SSD and SATA into my desktop system shortly. I will continue to use the SATA for archival. I'll use the flash SSD as a working set.
Do you have 15K 2.5" drives in your workstation already? I have 15K 3.5" drives for my working set.
However, if you're like me, you must know that you are most unusual. It's a niche, surely, but hardly the mass market.
C//
Re:OS patches? (Score:1, Insightful)
1. If what you say is true, then you are essentially arguing that a typical Linux user is better than a typical Windows user not because of technological advantages in Linux, but because of a social quirk. In essence, you just ceded the point you were arguing against: social engineering is a hole that no amount of technological boundaries can ever stop.
2. That said, I know a lot of people who switch to Linux, or to Mac, or to Firefox, or to some other miracle-pill software because they've heard it's more secure, and then they feel they don't have to take any real precautions or worse, they stop using the precautions they had been using. I'm not at all convinced that a user who migrates because they've heard Linux is secure is more savvy to social engineering in general.
That said, I agree that the average Linux user is probably more likely to think about security, using similar reasoning (but not quite the same). I think the OS/religious metaphor works really well here:
1. People who think for themselves are more likely to change OS, for any reason of their own.
2. More people started with Windows than any other OS.
3. Thinking for yourself is a trait assumed to be equally likely in people who started with Windows as in any other OS.
4. Therefore, all things being equal, people who think for themselves will leave Windows for an alternative, leaving a disproportionate number of people who don't think for themselves with Windows. Even if Windows does not make people fail to think for themselves.
For real fun, you can replace "Windows" with "Christianity" and I think the same basic argument holds up, leading to a migration of intelligent, independent thinkers to atheism which does not actually indicate that atheism causes better thinking. I think atheism is probably right, myself. Just sayin'.
Re:Flash memory? (Score:3, Insightful)
If you've still got an external(or internal) physical HDD, then SSD's have not taken over. They've become a part of a new solution, not replaced an old solution.
Re:Not to be confused with (Score:4, Insightful)
As a not so naive Brit, we have our much superior 3 second rule for the same thing.
I'd like to know what the GP has on the floors in his house that is so toxic that the tiny amount that will rub off on food is detrimental for your health? How on earth do people survive in places without nice sealed floors and cleaning chemicals? You'd think we'd have evolved some method of protecting our bodies against stuff like that.
Re:Not to be confused with (Score:2, Insightful)
> that's fallen on the floor if you pick it up fast enough?
Short answer: no, but yes.
Long answer: There are two kinds of people. Some people won't eat food that has fallen off the plate onto the table, their lap, the chair, the floor, wherever. If it fell, it's "dirty", and they throw it away.
There are also people who think this is silly. If there's no visible dirt on it, or if you can brush it off, hey, it's still food. Unless it fell into pig excrement or something, a little surface contact with a potentially dirty surface is fundamentally unimportant. Nothing the old stomach acid can't handle in short order.
The "thirty-second rule" arises from a clash between these two ways of thinking. Somebody drops a piece of food, picks it up, and eats it, but there's one problem: someone from the other school of thought is present, and shrieks out "Ewwwwwwww! That fell on the floooooor!" The other guy shrugs. "Yeah, so? It was only on the ground for, like, five seconds. What's your problem?"
In practice, the number of seconds doesn't matter. Most people who have a piece of food in their hand or on their plate with the intention of eating it have put more thought into wanting to eat the food than they have into being grossed out by the floor, so if they drop the thing, they pick it up and eat it without a second thought. If it takes them thirty-two seconds to pick it up instead of thirty, or six instead of five, or whatever the local variant of the "rule" is, they won't say, "Oh, it's been a couple of seconds too long, better throw it out." The thought process is more along the lines of "Hey, I wanted that; I didn't mean to drop that; I was going to eat that; give me that. Nom nom nom."
And going the other way, with a few exceptions, people who are grossed out by dropped food usually won't eat it if it only fell on the table or the kitchen counter. The table is "dirty", even if it was just bleached half an hour ago. The counter is "dirty" as far as the food off the plate is concerned, even if you set an apple there a moment ago (then picked it up and took a bite). The food fell, therefore it's contaminated, therefore you don't eat it.
Personally, I consider the whole "dropped food is gross" thing to be a minor neurosis, but not one that causes any significant trouble in a society with a long-term food surplus, such as the US for instance. If it makes you feel better to throw the food away, hey, toss it in the nearest waste receptacle. No skin off my nose.