Optane

Intel’s Optane: Two Confusing Modes. Part 3) App Direct Mode

Exploding HeadThis post is a continuation of a four part series in The SSD Guy blog to help explain Intel’s two recently-announced modes of accessing its Optane DIMM, formally known as the “Intel Optane DC Persistent Memory.”

App Direct Mode

Intel’s App Direct Mode is the more interesting of the two Optane operating modes since it supports in-memory persistence, which opens up a new and different approach to improve the performance of tomorrow’s standard software. While today’s software operates under the assumption that data can only be persistent if it is written to slow storage (SSDs, HDDs, the cloud, etc.) Optane under App Direct Mode allows data to persist at memory speeds, as also do other nonvolatile memories like NVDIMMs under the SNIA NVM Programming Model.

App Direct Mode implements the full SNIA NVM Programming Model described in an earlier SSD Guy post and allows software to Continue reading

Intel’s Optane: Two Confusing Modes. Part 2) Memory Mode

Exploding HeadThis post is the second part of a four part series in The SSD Guy blog to help explain Intel’s two recently-announced modes of accessing its Optane DIMM, formally known as the “Intel Optane DC Persistent Memory.”

Memory Mode

The most difficult thing to understand about the Intel Optane DC Persistent Memory when used in Memory Mode is that it is not persistent.  Go back and read that again, because it didn’t make any sense the first time you read it.  It didn’t make any sense the second time either, did it?

Don’t worry.  This is not really important.  The difficulty stems from Intel’s marketing decision to call Optane DIMMs by the name “Intel Optane DC Persistent Memory.”  Had they simply called them “Optane DIMMs” like everyone expected them to then there would have been Continue reading

Intel’s Optane: Two Confusing Modes. Part 1) Overview

Exploding HeadIntel 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 Continue reading

What is SNIA’s Persistent Memory Programming Model?

SNIA Persitent Memory Summit LogoIn this post The SSD Guy will discuss the SNIA Nonvolatile Memory (NVM) Programming Model, a framework to allow standard applications to take advantage of nonvolatile, or persistent, memory in any system that includes persistent memory,

This model is enormously important to the future of computing, yet few people even know that it exists.  It’s a fundamental change to the way that application programs access storage that will have significant ramifications to computer architecture and performance over the long term.

Here’s why: The industry is moving towards larger-scale systems that mix persistent memory with standard DRAM into a single memory address space.  Persistent memory has an advantage over volatile DRAM, since it maintains data after power is removed or lost.  Because of this certain application programs will want to know which memory is volatile and which is persistent and to take advantage of whatever persistent memory the system might provide.  I say “Larger-Scale” systems because small systems often combine Continue reading

An NVDIMM Primer (Part 2 of 2)

AgigA RamCardTwoThis post is the second of a two-part SSD Guy series outlining the nonvolatile DIMM or NVDIMM.  The first part explained what an NVDIMM is and how they are named.  This second part describes the software used to support NVDIMMs (BIOS, operating system, and processor instructions) and discusses issues of security.

Software Changes

Today’s standard software boots a computer under the assumption that the memory at boot-up contains random bits — this needed to be changed to support NVDIMMs.  The most fundamental of these changes was to the BIOS (Basic I/O Subsystem), the code that “wakes up” the computer.

The BIOS is responsible for detecting all of the computer’s hardware and installing the appropriate drivers, after which it loads the bootstrap program from the mass storage device into the DRAM main memory.  When an NVDIMM is used the BIOS must Continue reading

An NVDIMM Primer (Part 1 of 2)

NVDIMMs are gaining interest lately, so The SSD Guy thought it might be worthwhile to explain both what they are and how NVDIMM nomenclature works.

As I was writing it I noticed that the post got pretty long, so I have split it into two parts.  The first part explains what an NVDIMM is and defines the names for today’s three kinds of NVDIMM.  The second part tells about software changes used to support NVDIMMs in BIOS, operating systems, and even processor instruction sets.  It also discusses the problem of security.

In case the name is unfamiliar, NVDIMM stands for “Nonvolatile Dual-Inline Memory Module.”  Standard computer memory – DRAM – is inserted into the system in the DIMM form factor, but DRAM loses its data when power is removed.  The NVDIMM is nonvolatile, or persistent, so its data remains intact despite a loss of power.  This takes some effort and always costs more for reasons that will be explained shortly.

Although might seem a little odd to discuss memory in a forum devoted to SSDs, which are clearly storage, the NVDIMM is a storage device, so it rightly Continue reading

Comparing Wear Figures on SSDs

DWPD TBW GB/Day TriangleI have been receiving questions lately from people who are puzzled when companies use different parameters than their competitors use to specify the endurance of their SSDs.  How do you compare one against the other?  Some companies even switch from one parameter to another to define the endurance of different SSDs within their product line.

I have found that Intel uses three different endurance measures for its products: DWPD (drive writes per day), TBW (terabytes written), and GB/day.

There’s not any real difference between any of these measures – each one is one way of stating how many times each of the SSD’s locations can be overwritten before the drive has gone past its warrantied life.

The relationships between these three measures are illustrated in this post’s graphic.  You can click on it to see an expanded version.  It’s all pretty simple.  We’ll spell out the relationships in detail below, but in brief, if you want to compare Continue reading