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#32
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SATA Drives
pjp wrote:
I was doing some board level coding for a compnay long time ago now and we ended up with a batch of bad memory chips. They'd work ok "when working" but leave them sit awhile and you did not get back what you wrote. Was a pita to find and chips became worthless. DRAM needs to be refreshed, and that's what happens when you don't set the autorefresh timer to the correct value. Paul |
#33
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#34
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On 1/6/19 5:31 AM, joe wrote:
On 1/5/2019 10:33 PM, Jim H wrote: On Sat, 5 Jan 2019 00:19:37 -0800, in , Mike wrote: MTBF doesn't mean that YOUR device will last that long, or even close to that long.Â* All it means is that, if you have a large number of them, about half of them will die before MTBF. Are you feeling lucky? You can wish that's what the MTBF figure tells you, but in reality the probability of your device lasting as long as the MTBF figure is more like 37%. Only if you assume the failure rate is constant over time and there are no wear out mechanisms. Discussing MBTF is a way to start a flame war with those who have never done an MBTF study and do not know what it means. Basically, it means that if you put that many devices in front of you on a test bench, one is predicted to fail in a hour/year/ whatever. It is not a very good number to count on. It just sound great to hear you have a 1 million in the number. I did MBTF studies for the military years ago. Pretty much worthless. Here is a good article on it: https://www.bmc.com/blogs/mtbf-vs-mt...ts-difference/ My advice is to look at the warranty. That will give you a good estimate of how long things are expected to last. In college, we were taught to put the warranty at 90% of useful lifespan. But be aware that a lot of folks don't put the effort in to figuring out what their useful lifespan is, so they put down one year or something competitive sounding. Intel's SSD have a 5 year warranty, but crap out (brick) a lot sooner than that. |
#35
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On Mon, 7 Jan 2019 01:17:07 -0800, T wrote:
I did MBTF studies for the military years ago. Pretty much worthless. Especially to those looking for MTBF numbers! |
#36
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mechanic wrote:
On Mon, 7 Jan 2019 01:17:07 -0800, T wrote: I did MBTF studies for the military years ago. Pretty much worthless. Especially to those looking for MTBF numbers! On subsystems with mixed hardware/firmware, the numbers are also misleading, because they suggest we know how to quantify firmware failures. Seagate had some hard drives that would "brick" after 30 days of usage. This wasn't a seized motor, or a broken arm or flex cable, this was a firmware failure. The drives were actually recoverable... with a complicated procedure that involved starting the hard drive, with the controller board unscrewed and not touching the connection to the heads. It also required connecting a three wire, TTL level, serial port to the controller board and typing a cryptic set of commands. The MTBF number would not cover the failure in that case of the Seagate drive. And for some of the stuff we worked on, one of the reliability staff just pulled a number out of the air and said for all we know, firmware failures for a product could be 10x more prevalent than some other kinds of failures. It's not something that you could apply the "Easy Bake Oven" and do accelerated life testing. When you see those numbers for the products we buy, it's not really a proper portrayal of what could happen to them. It's like computing an MTBF for the hinge of one of the doors on your car, and using that as a metric for how long the whole car will last. It's like saying you have a 0.38% chance of getting cancer. It's a single point specification that doesn't take imponderables into account. It has virtually no predictive value. Some Seagate drives were "generally terrible", then another generation would come along where they were "good". The MTBF number on the datasheet for both products was the same. If my drive failed after 3 months, there wasn't much solace in that 1.5 million hour MTBF. In fact, the court of public opinion might be a better indicator of what to expect, than the math calc (a running average of experiences involving field data). I might be able to load my stock room with drives, based on how often other people were replacing theirs (2 to 3 years usage). If the pool of drives started off with the quality of this drive, it might be different. And this drive never parks the heads when it's not being used. The heads are always loaded on this drive. The other two drives in the computer use head parking, to extend their lives. This drive has no delay when you access it, and the motor sound doesn't change either (not a two-speed drive). Apparently every once in a while, they make a good drive. https://i.postimg.cc/rpJpKMTR/no-domino-flaws-here.gif The drive temperature is 22C, because an intake fan blows right across the surface of the drive. The bay covers were removed, and a framing and low speed fan fastened in front of the lower three bays. The optical drive at the top, works as normal (not part of fan scheme). The computer case is really old, and this fan is actually part of "general cooling" as opposed to being a "drive temperature experiment". The rear of the case has no exhaust fan, and you leave a slot or two open for exhaust (reduced backpressure). Paul |
#37
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On 1/6/2019 5:30 PM, Mike wrote:
snip We have very different views of reliability. If there's not enough oxygen, just don't breathe, makes about as much sense. 3000 erase-write cycles is a TINY number. The only way that works is if you don't do it. You seem fixated on a number. How long does it take, under normal use, to do 3000 erase-write cycles? Is it day, months, or many years? If the answer is many years, then does it really matter? They take Herculean measures to spread the wear and recover from bad data bits. From the user's standpoint, no effort is needed as that is all done in the SSD. snip |
#38
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On Sun, 6 Jan 2019 13:01:45 -0600, joe wrote:
On 1/6/2019 11:16 AM, Wolf K wrote: On 2019-01-06 08:31, joe wrote: On 1/5/2019 10:33 PM, Jim H wrote: On Sat, 5 Jan 2019 00:19:37 -0800, in , Mike wrote: MTBF doesn't mean that YOUR device will last that long, or even close to that long.* All it means is that, if you have a large number of them, about half of them will die before MTBF. Are you feeling lucky? You can wish that's what the MTBF figure tells you, but in reality the probability of your device lasting as long as the MTBF figure is more like 37%. Only if you assume the failure rate is constant over time and there are no wear out mechanisms. Seems to me that MTBF is testable, no assumptions required. I expect the published figure(s) to summarise the test results. Where are the stats? So, how would you test an SSD with 1.5 million hour MTBF? If you saw a device for which a 1.5 million hour MTBF was claimed, would you believe it? If my arithmetic is right, 1.5 million hours is over 160 years. How did they test it and determine that number? |
#39
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In article , wrote:
My advice is to look at the warranty. That will give you a good estimate of how long things are expected to last. In college, we were taught to put the warranty at 90% of useful lifespan. those are two separate things. But be aware that a lot of folks don't put the effort in to figuring out what their useful lifespan is, so they put down one year or something competitive sounding. Intel's SSD have a 5 year warranty, but crap out (brick) a lot sooner than that. they do not. intel ssds are very reliable. |
#40
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In article , Ken Blake
wrote: If you saw a device for which a 1.5 million hour MTBF was claimed, would you believe it? If my arithmetic is right, 1.5 million hours is over 160 years. How did they test it and determine that number? accelerated testing. |
#41
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nospam wrote:
In article , wrote: My advice is to look at the warranty. That will give you a good estimate of how long things are expected to last. In college, we were taught to put the warranty at 90% of useful lifespan. those are two separate things. But be aware that a lot of folks don't put the effort in to figuring out what their useful lifespan is, so they put down one year or something competitive sounding. Intel's SSD have a 5 year warranty, but crap out (brick) a lot sooner than that. they do not. intel ssds are very reliable. http://knowledge.seagate.com/article...S/FAQ/174791en "Seagate's new standard is AFR" "The product shall achieve an Annualized Failure Rate - AFR - of 0.73%" https://www.networkworld.com/article...ssd-myths.html "Exhaustive studies have shown that SSDs have an annual failure rate of tenths of one percent, while the AFRs for HDDs can run as high as 4 to 6 percent." === Boo! and/or Hiss! You can see in a slap-fest, there is plenty of slapping to go around. Not too much weight should go into believing in hyperbole, except what your own experience shows. If you had an OCZ SSD brick on you, you're less likely to believe the "tenths of one percent" thing :-) (Back in the era where they still couldn't write firmware.) One of the people in the newsgroup had a brickage over night (wouldn't work the next day). And at the time, the adoption rate for SSDs was still pretty low. Once you discount the wear mechanism of Flash chips, and assume the critical data storage area in an SSD is made of "sparkle ponies", I'm sure you'll be hitting an AFR of "tenths of one percent" :-/ If you discount every possible failure mechanism, then it cannot fail!!! Quick! Somebody get me the number-grinder, to grind me some new numbers. Even in the current day, firmware could still be an issue. If the failure rates are low, we might not even notice there's an issue. Paul |
#42
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In article , Paul
wrote: https://www.networkworld.com/article...ng-ssd-myths.h tml "Exhaustive studies have shown that SSDs have an annual failure rate of tenths of one percent, while the AFRs for HDDs can run as high as 4 to 6 percent." === Boo! and/or Hiss! from that link, And since SSDs contain billions of cells, we¹re talking about an enormous amount of data that can be written and deleted at every moment of every day of the drive¹s life. For example, one 100GB SSD that offers 10 drive writes per day can support 1TB (terabyte) of writing each and every single day, 365 days a year for five years. very few people write a terabyte *every* *day*. a more realistic amount would be in the range of 10 gigabytes, which would put the lifetime (based on writes) at 500 years. something *else* is likely to fail first, including the user, who won't live anywhere near that long. tl;dr - ssds are *very* reliable. |
#43
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On 1/7/2019 10:51 AM, nospam wrote:
In article , Paul wrote: https://www.networkworld.com/article...ng-ssd-myths.h tml "Exhaustive studies have shown that SSDs have an annual failure rate of tenths of one percent, while the AFRs for HDDs can run as high as 4 to 6 percent." === Boo! and/or Hiss! from that link, And since SSDs contain billions of cells, we¹re talking about an enormous amount of data that can be written and deleted at every moment of every day of the drive¹s life. For example, one 100GB SSD that offers 10 drive writes per day can support 1TB (terabyte) of writing each and every single day, 365 days a year for five years. very few people write a terabyte *every* *day*. Help me with the math. Maybe this is a video surveillance system. I get a new 100GB SSD and write 100GB to it. How many times did I erase each cell? over the next 2.4 hours, I overwrite all that data. How many times did I erase each cell? 2.4 hours later, I have overwritten all that data. How many times did I erase each cell? Keep it up 10 drive writes per day. .. .. .. ..until it fails. What's the write amplification? How long did that take? That's a limit case. The other end is don't write it at all. What's the shape of the life curve between those limits based on size and number of writes and unused capacity on the drive and how you TRIM it and and and... I expect my spinner to be more or less independent of all that. My SSD is a complex web of secrets hiding a fundamental defect in the storage method that's getting worse with each generation as geometries decrease and bits per cell increases. Start up resource monitor and look at disk writes. There are a LOT of writes due to system management. A LOT! They may not be big writes, but if there's no available space, my SSD has to move something to do it. All those small writes may be amplified significantly when it comes to SSD erase cycles. I don't have a number, but it does make me cautious. In terms of actual bytes written by applications, my TV time shifter writes about 30GB a day. I expect it would have to be TRIMmed frequently. No idea how expensive a TRIM operation is in terms of erase cycles at that level. I'm not anxious to put a SSD there. a more realistic amount would be in the range of 10 gigabytes, which would put the lifetime (based on writes) at 500 years. something *else* is likely to fail first, including the user, who won't live anywhere near that long. tl;dr - ssds are *very* reliable. |
#44
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On 1/7/2019 5:27 AM, joe wrote:
On 1/6/2019 5:30 PM, Mike wrote: snip We have very different views of reliability. If there's not enough oxygen, just don't breathe, makes about as much sense. 3000 erase-write cycles is a TINY number. The only way that works is if you don't do it. You seem fixated on a number. How long does it take, under normal use, to do 3000 erase-write cycles? That's the root of the questions. The answer is that it appears to be a very strong function of things known only to the drive vendor and whether that plays nice with the OS and the APPS. Is it day, months, or many years? If the answer is many years, then does it really matter? Not at all. Just convince me that it really is many years. They take Herculean measures to spread the wear and recover from bad data bits. From the user's standpoint, no effort is needed as that is all done in the SSD. I think you can say that for drives that are properly interfaced with the OS. In the end, it's not whether I have to interact with it while it's wearing out. The issue is that it's wearing out at all. snip |
#45
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