- Now that persistent memory has moved from a “wouldn’t it be great if we had this?” concept to a “we have some options, now what?” debate…. We need to define “persistent memory” based on the new reality. Rob Peglar and Stephen Bates reminded us that using the term SCM is not politically correct and can only be used in a safe space away miles from a SNIA conference (Starbucks Milpitas worked for me). This is good since it was way too vague and theoretical. Andy Rudoff offered a simple definition: it needs to be address in load/store like memory (Not blocks and pages), and persistent. Speed is in the eye of the beholder but a year ago there was a definition of <2us latency in applications which I liked. The NVDIMM-N and NVDIMM-P definitions would indicate that it does not need to be one type of memory but is a DIMM or system. These simple definitions would seem to eliminate some products that are often referred to as “persistent memory” (side discussion)
- The most common persistent memory today arguably is NVDIMM-N which provides us with up to 32GB DIMMS that can be written to like DRAM but never lose data. The challenges here are that the use of DRAM for entire capacity plus NAND plus energy support leads to a high cost that is 3x or more per bit compared to DRAM. As a result, a small amount of systems (typically SANs) use them today. Multiple providers were at the conference and you can buy this persistent memory whenever you wish.
- Frank Hady presented Intel Optane Persistent Memory and the applications. Two modes, one is persistent memory (App Direct) and one is memory Mode (which loses data on power cycle). Memory mode is great for adding tons of memory that is somewhat slower and cheaper but it is not persistent per Intel documentation. This is poised to grow rapidly with Intel backing but it is off to a slow start. From talking to customers, most say they still can’t get Optane PM to build their own system and the availability today is running apps on cloud systems. I have details on modes and projected revenue in other publications
- NVDIMM-P is proposed as an open source version similar to Optane PM where the architecture supports some DRAM plus NAND or other memory type to optimize for cost. This will allow DIMMs that are LESS expensive than DRAM, higher density, and more non-proprietary options. We need this ASAP! When can I get one???
- From the conference, it feels like Infrastructure support and application drivers are ahead of the actual hardware…. This is probably not totally true but there is drive from Intel and SNIA to get all the support in place and the OS supports it and we have applications. Once Intel ships significant volume and competitors start shipping their versions of PM, we can test out all the applications
See more info on our blogs or website. Thanks to Chris Mellor of Register fame for republishing some of my FMS work on persistent memory and Optane with all the gory details and numbers.