On Nov 26, 2007, at 3:27 PM, David Mathog wrote:
I ran a little test over the Thanksgiving holiday to see how common
random errors in nonECC memory are. I used the memtest86+ bit fade
test
mode, which writes all 1s, waits 90 minutes, checks the result, then
does the same thing for all 0s. Anyway, this was the best test I
could
find for detecting the occasional gamma ray type data loss event. The
result: no errors logged in 5 solid days of testing. So this class of
error (the type ECC would detect and probably fix) apparently occurs
on these machines at a rate of less than 1 per 840 Gigabyte-hours.
Possibly the upper limit is half that if data can only be lost
on 1 -> 0 transition, or vice versa. This assumes the bit fade test
works, which cannot be independently verified from these results.
On the web there are references to an IBM study which found 1 bit
error/256Mb/Month, which would have been (.25 *30 * 24) =
1 per 180 Gigabyte-hours. If IBM's numbers held for my hardware
there should have seen 4 or 5 errors in total. Mine are in a basement
in a concrete building, perhaps that provided some shielding
relative to
what IBM used for their test conditions.
The memory was Corsair Twinx1024-3200C2. When first installed all
of this memory had run for 24 hours with no errors in normal
memtest86+ testing.
Regards,
David Mathog
Or maybe you got lucky. Five days may not be long enough.
We have had customers report events that included parity errors on
hundreds of nodes simultaneously on large clusters. Higher altitude
makes things worse. Being in a DOE lab near lots of interesting
materials does not help either. :-)
Scott
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