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Nightmare - External hard drive crashes to floor
ark_ader:
--- Quote from: shmokes on February 22, 2010, 10:30:05 am ---
--- Quote from: Xiaou2 on February 22, 2010, 03:26:26 am ---
--- Quote ---All these specs assume you have a quality burner, which most people don't. For your cheapo $35 CD/DVD burner, quarter the lifetimes.
--- End quote ---
Heh. Thats Scammer Info IMOP. Prove it with any form of Logic.
--- End quote ---
It's not really a fair challenge cos you are limiting him to logic and not evidence, when the obvious method of proof here would be citation rather than argument. ;D
--- End quote ---
+1 :applaud:
MonMotha:
You asked for an explanation, so here's one, albeit a bit technical at times.
As a data point on flash memory retention, Google a datasheet for the MT29F1G08. This is a 1Gb (256MB) SLC NAND device from Micron that is reasonably mature (it's been out for several years). Micron recently placed all their NAND flash datasheets under NDA for some reason I can't comprehend, but this one's old enough that copies not covered by NDA are still floating around. The datasheet says 10 years over full temp range, which goes to 85C on the extended temp parts or 70C on the commercial temp parts. I've not known Micron to lie about things like this. They've been making memory devices (volatile and non-volatile) pretty much as long as such devices have existed. Can they 100% guarantee those specs? No; the parts haven't existed long enough. However, they do accelerated aging tests to arrive at those numbers, and I'd say they have the data to back those aging tests up. They spec these things out for military/aerospace use too, and those guys run their own independent tests to validate.
Do be aware that the higher density devices, even in SLC, sometimes have slightly lower reliability due to the smaller geometries. Generally, they make up for it by applying lots of ECC. MLC devices also can have lower reliability since they have to discriminate between 4 or 8 levels per cell rather than just 2. Again, these larger devices tend to have lots of ECC to mitigate this.
As another data point, the microcontroller I'm currently using from Atmel specifies 15 years flash data retention across operating temp range (-40 to +85C). Atmel's also been at this a while. Reliability of microcontrollers is generally taken to be a pretty freaking big deal, much more so than in the consumer market segment. These things get used in applications where failure could result in injury or death. Obviously, the designer of the device should (and generally does) take precautions to make the device "fail safe", but even then, failure is often costly.
In talking with my reps from various companies that do non-volatile memories, there is apparently something of an exponential relationship between temperature and retention. A device that retains 10 years at 85C may only last a few hours at 150-200C. There are often characterization charts that exceed the specified operating ranges kicking around inside semiconductor companies for many devices (yes, I've worked for one, and yes, I've seen such charts for various devices, though not flash memories). If you ask nicely (and often sign an NDA), you can often get access to those charts with the caveat that the data is not "guaranteed". Semiconductor companies take electrical performance characteristic guarantees very seriously. Guaranteed characteristics are generally valid all at once, so worst case across the board. I've never had a semiconductor device fail to meet basic electrical performance characteristics in a manner that wasn't disclosed as an errata. In general, devices VASTLY exceed their specified performance. I once ran a micro specified for 6MHz@5V at 20MHz@3V, though it couldn't go any higher, and I was operating it at room temp only. Generally, reliability problems are design related, but I have also found functional errata (the device does not behave entirely as described) before.
Most of the industry reports and technical literature I read seems to agree with these numbers. There are also flash device integrators out there who make SD and CF cards that will sell you devices with a warranty. These guys will say, for example, "5 years minimum retention at 85C or your money back plus losses incurred up to $X". Expect to pay a substantial premium for such devices just because of the insurance they have to carry, let alone to more rigorous design review and testing that goes into such devices, but such integrators do exist. The fact that people will put their money where their mouth is again says to me that the numbers are probably at least reasonable. Flash memory first started showing up in the mid to late 90s, and most of it is still happily chugging away, so a number of "10 years" is at least pretty well validated at this point without any accelerated testing.
As to optical media, my experiences are much more anecdotal. I do have media burned in the late 90s that still seems to read fine on various readers. You can get special "archival" media. Memorex has a "gold" line that they claim 300 years in highly controlled storage. I'd expect (though without any data to back it up) that a typical controlled home environment could get at least within an order of magnitude of that, so 30 years. I've got friends who have pulled out CDs from the early days of CD burners who can also still read them just fine. That's generally 10+ years. Your media lifetime will also be affected by data mode: CD-ROM or CD-DA. CD-DA has far less error correction on it due to the assumption that an incorrect bit here or there does not render the disc totally unusable (it just creates an audio artifact), while a single bad bit CAN render a CD-ROM useless.
Now, as to writer quality, that really is just based upon my experiences, I'll admit. The "quarter the lifetime" suggestion was an attempt to be conservative in the resulting media lifetimes. After all, if you expect it to last 10 years but it lasts 40, you probably won't complain. If you expect 40 but only get 10, you may be in trouble. However, my reasoning on doing this is based upon actual experience. My discs burned on quality burners all still seem to work, but I do have discs burned with cheap writers that are unreadable after 3-6 years of reasonable storage (though I'll admit that they are in general also on crappy media). I've also noticed that newer, cheaper writers are more likely to create discs which have trouble being read by other devices (especially standalone CD players) even when writing at slower speeds. My old Plexwriter 16/10/40A seems to be able to write the cheapest media I throw at it at 16x and produce something that reads on pretty much everything I chuck that disc into (from standalone players to other burners to CD-ROM drives that have seen 10 years of arcade duty) with no issues. Again, anecdotal I know, but it at least suggests that there is a difference. I've read some articles to this effect as well, but nothing scholarly (though I'm guessing something is available).
Xiaou2:
--- Quote ---I just don't think you're the god that you claim to be.
--- End quote ---
Heh. I dont think Ive ever claimed myself as any form of Deity lol. But man, Im somewhat
flattered that you credit me so high, to be that jealous. Im just some guy whos average at some
things, and have been dedicated enough to get very exceptional in other areas.. much the same as
many others out there who you may be jealous of.
I do have gifts in some areas, such as design/art, spatial awareness, heightened awareness
thru ability to make associations, and mechanical ability... but for all my gifts, I have a slew of
problems which darken my days. Poor memory retention, a hair of OCD (which causes mild depression at times), poor level of ability to fully understand complex information... so will never be
a programmer, do complex maths, etc.
Health isnt the greatest. Tired too much. (poor ability to process food to energy?) Horribly crooked teeth I cant afford to fix. Larger pores which cause me to often get 2 whiskers growing
out of one pore... ugg
Basically, Im Human, like everyone else.
--- Quote ---It's not really a fair challenge cos you are limiting him to logic and not evidence, when the obvious method of proof here would be citation rather than argument.
--- End quote ---
Heh. I guess so :) But...
I seriously doubt anyone will be able to dig up actual proof that one burners 'Burned Cd' will last
less years than a higher priced burner, which is exactly why I asked for some sort of Logical
reason for that.
There IS physical proof that the MEDIA you burn on your plays the biggest role in data lastability.
If you buy a DVD movie at the store, that DVD will have been burned with a different type of
media than what they sell at the stores for your PC burner. Of course, the burners they used to
burn those discs are different too.. But if you put the PC media discs into them, them will
fail just as fast as a cheap home burner.
A burner is simply a laser that burns pits into a surface. The pits are no different from
a pro burner, than a home burner, ...else they would not be able to be read by the same types
of players.
A pit does not change over time based on the quality of Laser that burned it. The only thing
that can change, is if the surface the data is on, is scratched/flaked off. (which happens on
cheaper media, or simply media meant for home burners)
So, If Im missing something here... then correct me... but logically, that theory that a
$200 burners burned cds will last longer than a $50 burners cds... is IMOP, seriously flawed.
MonMotha:
The issue is that some burners may create a better transition in the media than others (the media quality obviously has a lot to do with this, as well). The higher quality transition has more margin for error than does the lower quality one meaning that it is more likely to be able to be recovered properly given the same amount of media degradation. This is generally true of any storage medium (optical, magnetic, electrical e.g. flash, ink on paper, chiseled wood, etc.). The better your SNR to start, the more margin you have for recovery. Now, whether or not cheap burners have less margin to begin with than more expensive/higher quality models may be questionable, but my experience has been that there is, indeed, some sort of phenomenon along these lines going on.
Imagine my goal is to burn a hole in a piece of quad-rule graph paper using a laser. If a square has a hole in it, that's a 1. If it has no hole, that's a zero. I need a laser powerful enough to actually burn a hole in it, but not so powerful that it just sets the whole piece of paper on fire. Furthermore, I need to control the size of the hole. Over time, the holes will either get bigger or they may get plugged with debris. I need a hole that's big enough to be reliably seen but no so big that it causes adjacent squares to also look like they have a hole burned in them even if they were not intended to. You can see how my laser power would have an effect here. Same goes for CD media, but the squares are way smaller, and you're just causing a change in reflective/diffractive properties by deforming or ablating a dye layer rather than burning a hole straight through the thing.
shmokes:
I don't know much about this, but I can at least hypothesize about scenarios in which you would be wrong.
First, it's important to understand that commercial DVDs and CDs (i.e. movies and music) are NOT burned. They are pressed. An image of the data is tooled and physically stamped into the polycarbonate to create the permanent pits that make up the little 1s and 0s. Since pressing DVDs at home is not feasible they needed another method, hence the burners. But the burners don't burn pits right into the plastic to mimic what's going on with the commercial DVDs and CDs. The laser inside a burner isn't nearly that powerful. Instead, DVD-Rs and CD-Rs have a layer of dye in them that reacts to the laser; the laser turns the dye opaque if I'm not mistaken. This dye isn't nearly so robust as a physical pit pressed into the plastic, which is what makes a commercial disc so much sturdier and more reliable than one burned at home.
So, with that in mind I would suggest (mind you without any basis) that perhaps the dye layer reacts differently to different intensities of laser. For example, maybe the spec calls for the dye to be heated to 200 degrees in order to trigger the effect that turns the dye opaque. This is a spec that produces highly consistent and relatively permanent results. But maybe using a cheaper to manufacture laser that only heats the dye to 180 degrees turns out discs that work nearly as often, but the dye is more likely to revert back to its previous state, or simply fade into something unreadable in a shorter period of time.
I have no idea if this is the case, but it or something like it seems at least plausible. In other words, without more I see little reason to dismiss the possibility out of hand.
edit: heh . . . I hadn't read MonMotha's post when I posted, but it's pretty close to what I was guessing at
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