The Memory/Storage Hierarchy
It recently dawned on me that one of the charts that I most frequently use in my presentations has never been explained in The SSD Guy blog. This is a serious oversight that I will correct with this post.
The Memory/Storage Hierarchy (also called the Storage/Memory Hierarchy, depending on your perspective) is a very simply way to explain why there are multiple memory and storage types within a system: Why is there a cache memory, or a DRAM, or an HDD? The simple answer is that you can improve the system’s cost/performance ratio of you break the system down into an appropriate mix of fast & slow, expensive & cheap memory or storage.
To explain this I go way back to the 1960s and review the concept of “Virtual Memory”. This concept was first commercialized by computer maker Burroughs, although it was first implemented by the University of Manchester in England. The basic concept was to provide programmers with an extraordinarily large memory in which to run their programs by fooling the program into thinking that the memory was as large as the magnetic disk.
I actually look at it from Continue reading
Podcast: Flash Memory Summit 2019
Those of you who enjoy listening to podcasts may want to hear Ray Lucchesi (Silverton Consulting) and Keith Townsend (The CTO Advisor) interview The SSD Guy for their series “Greybeards on Storage.”
This interview is the series’ 86th episode covering the world of storage. These guys do a fantastic job of probing this industry with great enthusiasm and insight.
This episode is a 40-minute compendium of the sights and goings-on at the August 2019 Flash Memory Summit along with observations on the industry in general. It’s not strictly structured, and not strictly serious, but just three industry insiders having a lot of fun sharing their observations.
Some of the broad range of subjects that Continue reading
Start-Up Fadu Launches New SSD Controller
Fadu, a startup out of Korea, made a big splash at the Flash Memory Summit to announce its new NVMe SSD controllers that don’t compromise speed to achieve low-power operation.
The company’s products are focused on quality of service (QOS) in enterprise-style 24/7 workloads with the aim of enabling the transition to NVMe in Enterprise and Hyperscale data centers, the fastest-growing segments in the SSD market. Some readers may recall that Fadu won the 2018 FMS Best-of-Show award in the “Most Innovative Flash Memory Technology” category for an earlier generation of products.
The company’s founding team comes from Samsung and Hynix with a CEO (Jihyo Lee) from Bain Capital. Lee gave a keynote address at the Flash Memory Summit simply titled: “Enterprise SSD: The Future”
The new SSD controller, Annapurna, is a Continue reading
Intel’s Optane: Two Confusing Modes. Part 4) Comparing the Modes
This post completes The SSD Guy’s four-part series to help explain Intel’s two recently-announced modes of accessing its Optane DIMM, formally known as the “Intel Optane DC Persistent Memory.”
Comparing the Modes
In the second and third parts of this series we discussed Intel’s Memory Mode and the company’s App Direct Mode. This final part aims to compare the two: When would you use one and when the other?
There’s really no simple answer. As with all benchmarks, certain applications will perform better with one mode than with another, while other applications will behave the opposite way. Adding to the problem is the fact that App Direct Mode actually supports not one but four different access methods, which will be further explained below. As a rule of thumb performance for large serial accesses might be Continue reading
Failure is Not an Option — It’s a Requirement!
I was recently reminded of a presentation made by GoDaddy way back in the 2013 Flash Memory Summit in which I first heard the statement: “Failure is not an option — it is a requirement!” That’s certainly something that got my attention! It just sounded wrong.
In fact, this expression was used to describe a very pragmatic approach the company’s storage team had devised to determine the exact maximum load that could be supported by any piece of its storage system.
This is key, since, at the time, GoDaddy claimed to be the world’s largest web hosting service with 11 million users, 54 million domains registered, over 5 million hosting accounts, with a 99.9% uptime guarantee (although the internal goal was 99.999% – five nines!)
The presenters outlined four stages of how validation processes had Continue reading
Intel’s Optane: Two Confusing Modes. Part 3) App Direct Mode
This 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
HDD & SSD Combined Into One
The SSD Guy has often explained to readers that the storage industry is caught between two alternatives: fast and costly, or cheap and slow. This is the key difference between SSDs and HDDs. I have recently learned of a new secret government research effort, code named “SiliDisk,” that will provide the best of both worlds by marrying flash memory with the mechanics of an HDD.
The approach is incredibly ingenious, while remaining deceptively simple: All that is required is to replace the disks in an HDD with the wafers used to manufacture NAND flash. Both are round, so there’s little engineering effort to switch from a magnetic disk to a flash wafer.
The NAND flash on the wafer is almost completely standard. The only two changes are that the chips aren’t scribed or sawn apart, saving a small sum, but a hole must be etched through the center (which can be seen in the photo below) offsetting this savings. The HDD mechanisms are unchanged with one exception: While today’s HDDs are largely manufactured using 2.5″ and 3.5″ platters (65mm & 90mm), NAND flash is exclusively produced on 300mm wafers. This means that Continue reading
Intel’s Optane: Two Confusing Modes. Part 2) Memory Mode
This 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
What is an SSD Trim Command?
Although the Trim command has been defined for nearly a decade, for some reason I have never written a post to explain it. It’s time for that to change.
Trim is something that was never required for HDDs, so it was a new command that was defined once SSDs became prevalent. The command is required because of one of those awkward encumbrances that NAND users must accommodate: Erase before write.
NAND flash bits cannot be altered the same way as an HDD. In an HDD a bit that’s currently set to a “1” can be re-written to a “0” and vice versa. Writing a bit either way takes the same amount of time. In NAND flash a 1 can be written to a zero, but the opposite is not the case. Instead, the entire block (4-16k bytes) must be erased at once, after which all bits are set to a 1. Once that has been done then zeros can be written into that block to store data. An erase is an excruciatingly slow operation, taking up to a half second to perform. Writes are faster, but they’re still slow.
Let’s say that a program needs to Continue reading
Intel’s Optane: Two Confusing Modes. Part 1) Overview
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 Continue reading
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