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

3D XPoint Memory at the Storage Developer’s Conference

3D XPoint Report GraphicThis Sunday (Sept. 20, 2015) I will be presenting my company’s findings on the 3D XPoint memory that was introduced by Intel and Micron in July.  I will be speaking at the Storage Networking Industry Association (SNIA) Storage Developer Conference (SDC) Pre-Conference Primer.  You can click the name  to be taken to the agenda.

This won’t be the only talk about persistent memory technology at the conference.  Prior to my presentation storage consultants Tom Coughlin and Ed Grochowski will give an overview of advances in nonvolatile memories, and following my presentation will be two Intel talks.

Intel will be covering this new technology a lot during the conference.  Of a total of 120 presentations at the conference and pre-conference primer, Intel will be presenting nine, seven of which directly name persistent memory or nonvolatile memory in the title.  Other firms will also be talking about NVM: AgigA, Calypso, HP, Pure Storage, and SMART Modular.  Even Microsoft alludes to it in a couple of its presentation titles.  Persistent memory is a hot issue.

So, the question for readers of The SSD Guy blog is: “Will this do away with SSDs?”

This is a question that was Continue reading

Understanding Storage Delays

Jim PappasJim Pappas of Intel, a fellow member of SNIA (the Storage Networking Industry Association) shared a really intuitive way to understand storage delays at the last Storage Developer Conference (SDC).  It’s very simple.  First consider these two facts:

  • The difference between the speed of system memory and that of a hard disk drive (HDD) is roughly 6 orders of magnitude, or 1 million times
  • SSDs split the gap.  An SSD is about 1,000 times faster than an HDD, and is about 1,000 times slower than system memory.  Memory access times are measured in nanoseconds (ns), SSDs in microseconds (µs) and HDDs in milliseconds (ms)

The problem with understanding this (ns, µs, ms) is that Continue reading

Intel Intros Fast Datacenter SATA SSD

IOPS Over Time - Competing SSD vs. Intel DC S3700Today Intel announced a new SATA III SSD, the DC S3700 Series.  The new product is fast, supporting 75,000 random 4K read IOPS and 36,000 random 4K write IOPS.  Average read latency is 45microseconds (µs) with writes averaging 65µs.  Sustained sequential reads are 500 megabytes/sec with sustained sequential writes at 460.  The read performance of this SSD, although a SATA device, is twice that of Intel’s 710 PCIe SSD announced in April, and writes are a full 15 times faster.  Intel calls this performance: “Scary fast!”

Intel says this device is its best Continue reading

19nm & 20nm SSDs Arrive!

Toshiba 19nm vs. IMFT 20nm NAND Processes (Courtesey Techinsights and Toshiba)SSD-watchers have expressed some concern over the last few years that  SSDs cannot be manufactured using advanced NAND flash process geometries.  This is because these parts have lower endurance and a larger number of bit errors than NAND made using less-advanced processes – the tighter the process, the shorter the flash’s life, and the more errors it will have.

Fortunately these concerns seem to be Continue reading

Apple’s Fusion Drive – An SSD Cache for the Macintosh

Apple's Chart of Fusion Drive Performance for the new Mac MiniOn October 23 along with the highly-anticipated announcement of the iPad 4, Apple rolled out new Macintosh computers that for the first time in an Apple product pairs an SSD with a conventional HDD to get the best combination of capacity, speed, and price.  The company calls this its Fusion Drive, not to be confused with Fusion-io’s highly-regarded products.

The SSD Guy did not attend the announcement, and there is little on the Apple website.  I contacted Apple, and they don’t have very much detail to share at this time.  This is important to note, since Continue reading

How Controllers Maximize SSD Life – Better Wear Leveling

Tempus FugitIn this post we will explore how the right wear leveling algorithm  can help a controller maximize the life of an SSD.

Wear leveling is a fact of life with NAND flash – blocks start to suffer bit failures after a certain number of erase/write cycles (usually specified from the thousands to the hundreds of thousands) and it is only natural that software will attempt to over-write some blocks more than others.  In order to prevent this from causing failures, all of today’s SSD, USB flash drive, and flash card controllers incorporate some sort of wear leveling.

This is a simple re-mapping of the contents of the flash chips.  A more graphical explanation is Continue reading

Seagate Updates Hybrid Drive

Intel/Seagate Demo of RST System Using a Hybrid HDDAt the Intel Developer Forum Intel showed Seagate‘s updated Momentus XT Hybrid Solid State Drive in operation.  The new drive is only 7mm thick, significantly thinner than the 9.5mm Momentus XT that the company has been shipping for the past 2 years.

This is significant because the 13mm target thickness of the Ultrabook platform is extremely difficult to achieve using a 9.5mm drive, yet the performance specification of the Ultrabook requires the use of NAND flash, either in the form of a full-blown SSD, an HDD with an additional cache SSD, or a hybrid drive.  Of the three choices, Continue reading