The end of the DAX experiment [LWN.net]

The end of the DAX experiment

Posted May 2, 2019 17:06 UTC (Thu) by Cyberax (✭ supporter ✭, #52523)
Parent article: The end of the DAX experiment

DAX doesn't exist anyway. You simply can't get DAX devices unless you are a big company that is ready to sign tons of NDAs and build a SKIF to work on the devices (might be exaggerating about SKIF a bit).

As a member of public, the most you can get are "emulators" - simple DRAMs with a battery backup.

And it's been going on like this for _years_ now.

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The end of the DAX experiment

Posted May 2, 2019 17:52 UTC (Thu) by brouhaha (subscriber, #1698) [Link] (5 responses)

Intel Optane DC persistent memory is supposed to be available next month, at around $900 for a 128G DIMM or $2700 for a 256G. Some retailers are taking preorders. No SCIF needed. :-)

The end of the DAX experiment

Posted May 2, 2019 17:57 UTC (Thu) by Cyberax (✭ supporter ✭, #52523) [Link] (4 responses)

I'll believe it when I see it.

Also, the quoted prices are actually _worse_ than the straight DRAM price.

The end of the DAX experiment

Posted May 2, 2019 21:48 UTC (Thu) by josh (subscriber, #17465) [Link] (3 responses)

Not according to https://www.tomshardware.com/news/intel-optane-dimm-prici...

What DRAM pricing are you basing that on?

The end of the DAX experiment

Posted May 2, 2019 21:54 UTC (Thu) by Cyberax (✭ supporter ✭, #52523) [Link] (2 responses)

Tom's pricing states that the 128Gb version is going to cost $695.

You can buy that much DRAM (one stick!) for around $500, though in the form of multiple sticks.

The end of the DAX experiment

Posted May 2, 2019 22:09 UTC (Thu) by josh (subscriber, #17465) [Link]

You can't get a single 128GB stick for anywhere close to that. Memory prices aren't linear by size.

The end of the DAX experiment

Posted May 2, 2019 22:12 UTC (Thu) by farnz (subscriber, #17727) [Link]

Multiple sticks doesn't help when you're DIMM slot limited, though - a single 128 GiB stick is still a lot more than the price of a single Optane 128 GiB stick.

Also, for the sort of systems that can take Optane, you'd be using RDIMMs; a quick check shows that 128 GiB of RDIMM DDR-4 is around $800, and takes 4 slots of the typical 16 you have on a board. So Optane is cheaper than DRAM, but not by a huge amount.

The end of the DAX experiment

Posted May 2, 2019 20:57 UTC (Thu) by SEJeff (guest, #51588) [Link]

Did you means SCIF, as in the place where TS/SCI documents are allowed? Come on, it isn't that secret. You just need a secret squirrel decoder ring, or just wait to buy some Optane persistent memory.

The end of the DAX experiment

Posted May 3, 2019 14:41 UTC (Fri) by luto (subscriber, #39314) [Link] (2 responses)

“Emulator?” A DIMM with a battery is an excellent DAX device. I suspect it’s considerably faster than Optane.

The end of the DAX experiment

Posted May 3, 2019 18:55 UTC (Fri) by Cyberax (✭ supporter ✭, #52523) [Link] (1 responses)

It's an emulator, emulators can be faster than the real hardware. I was hoping for much more from Optane, but for now it appears to be just slightly cheaper than DRAM while being much slower.

The end of the DAX experiment

Posted May 3, 2019 20:26 UTC (Fri) by luto (subscriber, #39314) [Link]

I think that it’s not an emulator in any respect. It’s not like Optane is somehow the real thing and battery-backed DRAM is pretending. The battery approach was also first.

In some sense, Optane is an emulator. The DIMM protocol was designed to model the way that DRAM works. I assume that Optane goes a bit out of its way to speak the same protocol.