Intel recently announced two operating modes for the company’s new Optane DIMMs, formally known as “Intel Optane DC Persistent Memory.” The company has been trying to help the world to understand these two new operating modes but they are still pretty baffling to most of the people The SSD Guy speaks to. Some say that the concepts make their heads want to explode!
How does Optane’s “Memory Mode” work? How does “App Direct” Mode work? In this four-part series will try to provide some answers.
Like all of my NVDIMM-related posts, this series challenges me with the question: “Should it be published in The SSD Guy, or in The Memory Guy?” This is a point of endless confusion for me, since NVDIMM and Intel’s Optane blur the lines between Memory and Storage. I have elected to post this in The SSD Guy with the hope that it will be found by readers who want to understand Optane for its storage capabilities.
Memory Mode is the easy sell for the short term. It works with all current application software without modification. It just makes it look like you have a TON of DRAM.
App Direct Mode is really cool if you have an application program that can use it because it accelerates storage. The first users will be companies that have top-to-bottom control of their software, like certain custom applications (closed systems) and hyperscale data centers (which are also closed!) The customized software that runs these systems can be endlessly updated without as many compatibility concerns as does commercial “Off-The-Shelf” software, and therefore can be updated more frequently and with less testing.
After some years there will be off-the-shelf software that can use App Direct Mode in Optane-based systems, but it will be smart enough to know whether or not the system has Optane DIMMs and will still work in older non-Optane DIMM environments. This flexibility will cause the software to be slower than it could be, but many of these application programs will still be significantly faster in an Optane-based system than software that does not use App Direct Mode.
For the near term, though, the bulk of Optane DIMM applications are likely to use the technology in Memory Mode, with App Direct Mode becoming increasingly popular only after application programs are updated to take advantage of it. I took this into account back in 2015 when publishing the industry’s first 3D XPoint Memory report and built the first publicly-available 3D XPoint forecast based on this understanding.
Both of these operating modes provide significant benefit to users, so I have no doubt that both will be very popular. I don’t see App Direct Mode threatening Memory Mode, each will find and maintain its own special niche. Perhaps “Niche” is the wrong word, though, since, over the long term, both may be adopted by the bulk of computing applications, but this will take a long time to happen, especially since the Optane DIMM is not supported by all Intel processors. In fact, at the moment, no commercially-available Intel CPU supports the Optane DIMM at all, but that should change soon.
This four-part series, published in early 2019, explores each of Intel’s two modes to explain what they do and how they work in the following sections:
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