10^11 cycles is not “practically unlimited endurance”, that’s less than a second of use at 1 GHz

adgjlsfhk1 3 days ago | parent | next [-]

You can't use a single cell of RAM at GHz frequencies. By the time you read a value and write another value back, you're talking about ~200ns so you are capped at ~5mhz writes (and anything that you are actually trying to access that quickly will be in caches anyway so your writes won't make it out to the DRAM unless you explicitly flush the caches)

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nomel 3 days ago | parent | next [-]

200ns seems a bit high. But, if you do the math, you'll find that's a practically negligible difference, at only 6 hours at 5MHz.

DRAM appears to be closer to 300 hours, at reasonable temperatures [1], at the worst case workload.

It would be interesting if Google released their failure rates, like they did with hard disk vs ssd.

[1] modeled failures, page 75: https://repository.tudelft.nl/record/uuid:e36c2de7-a8d3-4dfa...

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crote 2 days ago | parent | next [-]

Skimming through the linked paper, I can't actually find that claim being backed up anywhere?

The abstract does indeed say "It was found that the system reliability decreases to 0.84 after 1·10^8s at a stressing temperature of 300K", but I can't find anything close to that in the sections about Bias Temperature Instability or Hot Carrier Injection.

The only thing which to me looks close is the rather acute failure in the Radiation Trapping section - but that also states that the failure mode is dependent more on the total dose than time, and the total dose at which it fails is somewhere between 126 krad - 1.26 Mrad. For reference, a dose of 1 krad is universally fatal to a human.

In other words: don't put unshielded DRAM in a nuclear reactor?

	▲	nomel 2 days ago \| parent \| next [-]
		I included the page number with the link, to prevent this, and also noted that these were modeled failures. I had trouble finding any real world data, which is where the google comment came in.
	▲	2 days ago \| parent \| prev [-]
		[deleted]

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ahartmetz 3 days ago | parent | prev [-]

>DRAM appears to be closer to 300 hours

Yikes! Things that you don't necessarily want to know. Another one is that GPUs are released crawling with bugs - only the ones without cheap driver workarounds are fixed.

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deepnotderp 3 days ago | parent | prev [-]

Sure, but conventional DRAM endurance is 10^15 or more

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deckar01 3 days ago | parent | prev [-]

> >10^3s retention, >10^11 cycles endurance

The implication is that it can theoretically hold a value for 10^14s (~3 million years).

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crote 2 days ago | parent [-]

Yes, but most memory workloads don't store the same value for 15+ minutes at a time. And if you're using it as long-term storage (so basically a flash alternative) that 15-minute retention time is awfully low.

	▲	deckar01 2 days ago \| parent [-]
		Decades of research into optimizing DRAM refresh efficiency suggests that you don’t understand how the world is using DRAM.