Mark Gritter (markgritter) wrote,
Mark Gritter

Reality >>> Theory

Bianca Schroeder's talk on DRAM errors is worth watching. (Though it did remind me how annoying EE380 sessions could be--- it's generally not students asking the same question over and over, it's faculty or random people off the street.)

Old theory: Increased levels of heat cause errors, soft errors dominate and are randomly distributed. (Lab testing involves pointing a heat gun at a DRAM device...)

Actual measurements from Google's server farm:

* Heat is correlated with increased error rate but does not seem to cause it. Rather, increased utilization drives both.

* Hard errors probably dominate error count and drive most uncorrectable errors.

* Less than 20% (maybe as little as 8%) of DRAM components accounted for 95-98% of errors.

* Initial burn-in works (little infant mortality) but devices start to degrade after 10-16 months.

* Little difference in error rate across manufacturers. Increasing size affects error rate in unpredictable ways, often super-linearly.

Dr. Schroeder's other work on reliability is also interesting.
Tags: computers, hardware, measurement
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