Budget Backups: Which is better
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@ajstringham said:
Obviously the appliance is disk based, but for archiving and even rotating sets of archives, disk is still what I saw almost exclusively.
That didn't answer anything. You see fixed disk (arrays) or mobile disk (USB / IEEE 1394 / eSATA) for archiving?
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@Carnival-Boy said:
I don't believe that a @scottalanmiller completely made up figure is probably the best that I can get. 4% is also significantly higher than 3%, so maybe I'll go with that. I also don't accept that there is no such thing as wear and tear when hard drives are used - any physical device will suffer from this. I'm not a hard drive expert, but that's a basic law of physics.
Never said or suggested that there was no wear and tear. I said it was completely insignificant - which is a statistical fact and incredibly well established by every drive study. How do you think drives are expected to run 20 years or more but will experience noticeable wear and tear in just hours or days of usage? Those two things cannot go together.
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4% is not a reasonable failure number. 3% is a best case for the best drives. External USB arrays don't get those drives. 3% is not achievable by those drives even under ideal (fixed, datacenter) conditions.
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Failure rates vary a lot too. Google found 3%. Backblaze found even datacenters see 4.2%. That's with consumer drives from BB.
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@scottalanmiller said:
Never said or suggested that there was no wear and tear. I said it was completely insignificant - which is a statistical fact and incredibly well established by every drive study. How do you think drives are expected to run 20 years or more but will experience noticeable wear and tear in just hours or days of usage? Those two things cannot go together.
@ajstringham suggested there was no wear and tear. I don't understand your question. What do you mean they'll experience noticeable wear and tear in just hours?
Can you give me a link to a hard drive study saying wear and tear is a completely insignificant cause of failure? I'm only going on Wikipedia which talks about wear and tear and may be wrong, but it makes sense to me.
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@Carnival-Boy said:
@ajstringham suggested there was no wear and tear. I don't understand your question. What do you mean they'll experience noticeable wear and tear in just hours?
Ah, AJ might have overstated it. There is effectively no wear and tear, not that there is none. It's so trivial as any consideration of it is a complete waste. Expectation of 20+ years of wear and tear before wearing out is 7,300 days. Running as a backup system how many days does it run, maybe 30? 30 is completely non-noticeable out of 7,300.
My point is that you can't expect any measurable wear and tear in the time used as a backup system.
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@Carnival-Boy said:
Can you give me a link to a hard drive study saying wear and tear is a completely insignificant cause of failure? I'm only going on Wikipedia which talks about wear and tear and may be wrong, but it makes sense to me.
A link to what? There is no study needed for basic math. I'm lost as to what you are looking for. Just think about how wear and tear works on drives. No external source needed.
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Basic math? I'm talking about basic physics. If you run a physical device with moving parts for for 8,760 hours (one year 24/7) wear and tear will have a significant influence on the probability of it failing. I don't believe external environmental factors and shocks are 100% of the reason a drive will fail in these conditions.
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@Carnival-Boy said:
Basic math? I'm talking about basic physics.
I understand but basic physics says that wear and tear does not constitute "wearing out" for more than 7300 days of continuous usage. So the physics + math say that 30 days or so of usage is completely inconsequential in terms of wear and tear.
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@Carnival-Boy said:
I don't believe external environmental factors and shocks are 100% of the reason a drive will fail in these conditions.
I understand that.
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@scottalanmiller said:
4% is not a reasonable failure number. 3% is a best case for the best drives. External USB arrays don't get those drives. 3% is not achievable by those drives even under ideal (fixed, datacenter) conditions.
Who says 4% is not reasonable? Also, define failure. My understanding (please correct me if I'm wrong) is that a server will fail a drive if it reports a certain number of errors (or any errors?), but that doesn't mean the drive won't work or that the drive will have data loss does it? So many of my external drives may actually have errors (or have had temporary errors - the drive could fail to read, then try again and succeed) but they weren't errors that caused data loss (they weren't fatal errors) so were undetectable to me and didn't compromise my backups, even though a server would have failed them. To use our car analogy, a car can fail in lots of different ways without preventing you from completing your journey.
If 30% is realistic, then the probability of 17 drives (that's the number I get through a year) working without errors over the course of a year is 0.23%. Even with such a small sample size, that's a small enough number to make me doubt your figure. A 4% failure rate, gives me a 50% probability of being error free. Throw in dozens of laptops, and dozens of portable hard drives that I've looked after over the years, and 4% sounds a reasonable reflection of my experience, with a reasonably large sample size.
The figure that really matters is the probability of taking one of those drives after a site disaster and attempting a restore and having it fatally fail. I reckon that figure could be around 1%. I reckon human error is a much bigger risk to recovery failure than physical error (like the classic one of discovering you were using a cleaning tape as your backup).
