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Am 02.03.14 09:45, schrieb Philip Robar:
> On Sun, Mar 2, 2014 at 12:46 AM, Jean-Yves Avenard
> <jyaven...@gmail.com>wrote:

[ cut a lot not relevant to my comment ]

>> Bad RAM however has nothing to do with the occasional bit flip
>> that would be prevented using ECC RAM. The probability of a bit
>> flip is low, very low.
> You and Jason have both claimed this. This is at odds with papers
> and studies I've seen mentioned elsewhere. Here's what a little
> searching found:
> Soft Error: https://en.wikipedia.org/wiki/Soft_error Which says
> that there are numerous sources of soft errors in memory and other
> circuits other than cosmic rays.
> ECC Memory: https://en.wikipedia.org/wiki/ECC_memory States that
> design has dealt with the problem of increased circuit density. It
> then mentions the research IBM did years ago and Google's 2009
> report which says:
> The actual error rate found was several orders of magnitude higher
> than previous small-scale or laboratory studies, with 25,000 to
> 70,000 errors per billion device hours per mega*bit* (about 2.5-7 ×
> 10-11 error/bit·h)(i.e. about 5 single bit errors in 8 Gigabytes of
> RAM per hour using the top-end error rate), and more than 8% of
> DIMM memory modules affected by errors per year.

 Have you some *reliable* source for your claim in above paragraph?

 You say that an average 8 GB memory subsystem should experience 5 bit
 errors per *hour* of operation.

 On the other side you say (only) 8% of all DIMMs are affected per
 *year*.  I *guess* (and might be wrong) that the majority of installed
 DIMMs nowadays are 2 GB DIMMs, so you need four of them to build
 8 GB.  Assuming equal distribution of bit errors, this means on
 average *every* DIMM will experience 1 bit error per hour.  That
 doesn't fit.

 Today's all purpose PC's regularly ship with 8 GB of RAM, and modern,
 widely used operating systems, no matter which vendor, all make
 excessive use of any single bit of memory they can get.  Non of these
 have any software means to protect RAM content, including FS caches,
 against bit rot.

 With 5 bit errors per hour these machines should be pretty unusable,
 corrupting documents all day and probably crashing applications and
 sometimes the OS repeatedly within a business day.  Yet I am not aware
 of any reports that daily office computing ceased to be reliably
 usable over the last decade.

 So something doesn't fit here.  Where is (my?) mistake in reasoning?

 Of course, this does not say anything about ZFS' vulnerability to RAM
 errors compared to other system parts.  I'll come to that point in a
 different mail, but it will take a bit more time to write it up
 without spreading more uncertainty than already produced in this

 Best regards


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