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Taking an Accurate Look at SSD Write Endurance

Author:
Date: February 20, 2013
Subject: Editorial, Storage
Manufacturer: Various
Tagged: tlc, ssd, slc, mlc, endurance

Taking an Accurate Look at SSD Write Endurance

Last year, I posted a rebuttal to a paper describing the future of flash memory as ‘bleak’. The paper went through great (and convoluted) lengths to paint a tragic picture of flash memory endurance moving forward. Yesterday a newer paper hit Slashdot – this one doing just the opposite, and going as far as to assume production flash memory handling up to 1 Million erase cycles. You’d think that since I’m constantly pushing flash memory as a viable, reliable, and super-fast successor to Hard Disks (aka 'Spinning Rust'), that I’d just sit back on this one and let it fly. After all, it helps make my argument! Well, I can’t, because if there are errors published on a topic so important to me, it’s in the interest of journalistic integrity that I must now post an equal and opposite rebuttal to this one – even if it works against my case.

First I’m going to invite you to read through the paper in question. After doing so, I’m now going to pick it apart. Unfortunately I’m crunched for time today, so I’m going to reduce my dissertation into the form of some simple bulleted points:

  • Max data write speed did not take into account 8/10 encoding, meaning 6Gb/sec = 600MB/sec, not 750MB/sec.
  • The flash *page* size (8KB) and block sizes (2MB) chosen more closely resemble that of MLC parts (not SLC – see below for why this is important).
  • The paper makes no reference to Write Amplification.

Perhaps the most glaring and significant is that all of the formulas, while correct, fail to consider the most important factor when dealing with flash memory writes – Write Amplification.

Before geting into it, I'll reference the excellent graphic that Anand put in his SSD Relapse piece:

writeamplification2.png

SSD controllers combine smaller writes into larger ones in an attempt to speed up the effective write speed. This falls flat once all flash blocks have been written to at least once. From that point forward, the SSD must play musical chairs with the data on each and every small write. In a bad case, a single 4KB write turns into a 2MB write. For that example, Write Amplification would be a factor of 500, meaning the flash memory is cycled at 500x the rate calculated in the paper. Sure that’s an extreme example, but the point is that without referencing amplification at all, it is assumed to be a factor of 1, which would only be the case if you were only writing 2MB blocks of data to the SSD. This is almost never the case, regardless of Operating System.

After posters on Slashdot called out the author on his assumptions of rated P/E cycles, he went back and added two links to justify his figures. The problem is that the first links to a 2005 data sheet for 90nm SLC flash. Samsung’s 90nm flash was 1Gb per die (128MB). The packages were available with up to 4 dies each, and scaling up to a typical 16-chip SSD, that only gives you an 8GB SSD. Not very practical. That’s not to say 100k is an inaccurate figure for SLC endurance. It’s just a really bad reference to use is all. Here's a better one from the Flash Memory Summit a couple of years back:

flash-1.png

The second link was a 2008 PR blast from Micron, based on their proposed pushing of the 34nm process to its limits. “One Million Write Cycles” was nothing more than a tag line for an achievement accomplished in a lab under ideal conditions. That figure was never reached in anything you could actually buy in a SATA SSD. A better reference would be from that same presentation at the Summit:

flash-2.png

This shows larger process nodes hitting even beyond 1 million cycles (given sufficient additional error bits used for error correction), but remember it has to be something that is available and in a usable capacity to be practical for real world use, and that’s just not the case for the flash in the above chart.

At the end of the day, manufacturers must balance cost, capacity, and longevity. This forces a push towards smaller processes (for more capacity per cost), with the limit being how much endurance they are willing to give up in the process. In the end they choose based on what the customer needs. Enterprise use leans towards SLC or eMLC, as they are willing to spend more for the gain in endurance. Typical PC users get standard MLC and now even TLC, which are *good enough* for that application. It's worth noting that most SSD failures are not due to burning out all of the available flash P/E cycles. The vast majority are due to infant mortality failures of the controller or even due to buggy firmware. I've never written enough to any single consumer SSD (in normal operation) to wear out all of the flash. The closest I've come to a flash-related failure was when I had an ioDrive fail during testing by excessive heat causing a solder pad to lift on one of the flash chips.

All of this said, I’d love to see a revisit to the author’s well-structured paper – only based on the corrected assumptions I’ve outlined above. *That* is the type of paper I would reference when attempting to make *accurate* arguments for SSD endurance.

OCZ Technology Delivers Vertex 3 with 20 Nanometer Flash

Subject: Storage | February 19, 2013 - 02:47 PM |
Tagged: ocz, vertex 3, 20nm, mlc

SAN JOSE, CA—February 19, 2012—OCZ Technology Group, Inc. (Nasdaq:OCZ), a leading provider of high-performance solid-state drives (SSDs) for computing devices and systems, today announced a new 20 nanometer (nm) NAND flash version of its award-winning Vertex 3 SSD Series. The new Vertex 3.20 SSD is a 2.5-inch, 6Gbps SATA III-based Multi-Level Cell (MLC) drive that implements the feature-set of the Vertex 3 Series but is built around smaller, state-of-the-art NAND flash process geometry.

Being that the Vertex 3 Series is one of OCZ’s most popular SSDs to date, and has received numerous accolades from media reviewers globally, the implementation of 20nm NAND flash will extend its availability and enable mainstream users of mobile and desktop platforms to improve gaming, multimedia, and the overall computing experience over traditional hard disk drives (HDDs) and other competing SSDs. The Vertex 3.20 SSD will be available in 120GB and 240GB storage capacities, with 480GB capacities to follow soon.

Utilizing the proven and effective LSI SandForce® SF-2200 processor, the Vertex 3.20 SSD delivers exceptional performance of synchronous 20nm NAND flash supporting read bandwidth up to 550MB/s, write bandwidth up to 520MB/s, random read performance up to 35,000 input/output operations per second (IOPS), and random write performance up to 65,000 IOPS. It is also optimized to provide excellent endurance and reliability coupled with power efficiency.

“OCZ is always looking for ways to deliver superior solid state drive storage performance and features, as well as making this technology more accessible to the complete range of customers,” said Daryl Lang, Senior Vice President of Product Management for OCZ Technology. “The Vertex 3 has been a popular SSD series among consumers and implementing the newer, smaller process geometry will not only extend its life, but enables mainstream users with an excellent computing experience at a competitive price point.”

The Vertex 3.20 SSD is supported by a 3-year warranty to ensure customer satisfaction and will be available shortly through OCZ’s global channel in 120GB and 240GB storage capacities.

Vertex3_20.jpg

Source: OCZ Technologies

Revisit the Vector, it is worth it

Subject: Storage | February 15, 2013 - 04:26 PM |
Tagged: vector, ssd, sata, ocz, mlc, Indilinx Barefoot

Just in case you forgot how impressive the OCZ Vector 256GB is, Overclockers Club would like to remind you.  The Indilinx Barefoot 3 controller is matched with low cost 25nm MLC IMFT NAND modules and 512MB of DDR3-1600 RAM for a cache.  That translates to incredibly fast performance but without the high price of other drives.  The 256GB model sits currently just under $1/GB, it is not the least expensive SSD available but when you consider the speeds this drive operates at it is the best value.  Remind yourself where OCZ's Vector sits in the pack by reading on at OCC.

barefoot3_diagram-mod.png

"OCZ's Vector line of solid state drives is every bit the performer that the Vertex 4 drives are with very few exceptions. In many of the tests, the two fastest drives were the Vertex 4 and OCZ's latest Indilinx Barefoot 3-equipped Vector. The only real weakness I saw was that the Vector was less frugal with the CPU cycles than the other Indilinx equipped drives. OCZ's move to the Barefoot 3 controller is beginning to pay dividends as it uses the technologies it has available in-house after the Indilinx and PLX acquisitions. It's taken a while to go all-in but that time has come. As the first totally in-house designed controller from OCZ, it seems to have hit on a controller that does better at managing real world usage scenarios and handling both compressible and incompressible data streams.”

Here are some more Storage reviews from around the web:

Storage

Source: Overclockers Club

Forget Cherryville, here's Jaycrest

Subject: Storage | February 8, 2013 - 07:25 PM |
Tagged: SF-2281 controller, Jaycrest, Intel, 335 Series, 240 GB, 20nm

The Intel 520 and 335 series are very similar, both using the SF-2281 controller with the difference being the flash chips.  The 335 uses the newly designed 20nm MLC flash which gives both higher storage density, retains the same 3,000 Program/Erase cycles as the 25nm 520 and it keeps the cost of the drives down.  [H]ard|OCP put it through tests similar to the battery of benchmarks Al did and it will come as no surprise that their results were similar as well.  This drive is never going to beat flagship SSDs in terms of raw performance but for readers who are unwilling to spend top dollar for an SSD the Intel 335 series allows you to pick up a 256GB SSD for under $200 without sacrificing anything but a bit of performance in certain specific usage scenarios.

H_335.jpg

"Intel has released its new Intel 335 Series SSDs featuring 20nm MLC NAND and a SandForce SF-2281 processor. Its new MLC NAND boasts impressive power and write specifications. This SSD is geared for the budget market, but will it be able to compete with low-cost TLC alternatives?"

Here are some more Storage reviews from around the web:

Storage

Source: [H]ard|OCP

ADATA XPG SX900 128GB SSD Full Review - Low Cost SandForce

Author:
Date: February 6, 2013
Subject: Storage
Manufacturer: ADATA XPG SX900 Product Page
Tagged: sx900, ssd, sandforce, adata

Introduction, Specifications and Packaging

Introduction

With newer and faster SSDs coming to market, we should not forget those capable controllers of yesteryear. There are plenty of folks out there cranking out products based on controllers that were until very recently the king of the hill. Competition is great for the market, and newer product launches have driven down the cost of the older SandForce 2281 SATA 6Gb/sec controller. ADATA makes a product based on this controller, and it's high time we gave it a look:

130205-221436-4.13.jpg

The ADATA XPG SX900 launched mid last year, and was ADATA's first crack at the eXtended capacity variant of the SandForce firmware. This traded off some of the spare area in the interest of more capacity for the consumer.

Read on for the full review!

Intel Launches New 335 Series SSD In 180GB Capacity

Subject: Storage | February 5, 2013 - 03:16 AM |
Tagged: ssd, SandForce SF-2281, sandforce, mlc, intel 335, Intel

Intel has added a new drive to its existing 335 SSD series. The new drive offers up 180GB of storage, but maintains the same level of read and write performance as its larger 240GB sibling.

Intel 335 Series 180GB SSD.jpg

The 180GB version uses 20nm MLC NAND flash paired with a SandForce SF-2281 controller. According to the Intel-provided spec sheet (PDF), the new drive is capable of sustained read and write speeds of 500 MB/s and 450 MB/s respectively. Further, the drive maxes out at 42,000 random read IOPS and 52,000 random write IOPS.

The drive will come in the 2.5” form factor, but is 9.5mm thick (meaning it will not work in all notebooks). Reportedly, Intel has redesigned the casing to include a schematic/blueprint graphic alongside the Intel logo.

Intel rates the 180GB 335 series SSD at 1.2 million MTBF and is warranted for three years. The drive can currently be found online for around $180, making it right around the $1/GB mark. Interestingly, the larger 240GB model is currently retailing for around $195. Therefore, if you can spare the extra $15, the 240GB model is the better deal.

Source: Intel

Kingston updates their SSDNow lineup

Subject: Storage | February 4, 2013 - 02:09 PM |
Tagged: kingston, ssdnow v300, SF-2281 controller, mlc

Kingston's updated SSDNow V300 uses 19nm Toshiba Toggle NAND and the SandForce 2281 controller with some unspecified enhancements.  Kingston has made a name for themselves in the SSD market for offering an easy and fully explained upgrade path for users who are unfamiliar with changing hard drives.  The updated version is no different, included is an external enclosure for the SSD and a USB cable to allow users to easily copy over any data which is of great benefit for users who don't have several enclosures laying around.  [H]ard|OCP's testing showed that even though this is a value priced drive, it also performs better than a lot of the competition.

H_kingstonssdnow.jpg

"The Kingston SSDNow V300 is yet another value-oriented SSD in Kingston's wildly successful line of mainstream solid state drives. With the pressures of TLC SSDs squeezing the value market we take a look and see if a standard MLC SSD with 19nm Toshiba Toggle NAND and an SF-2281 processor can keep up with the changing times."

Here are some more Storage reviews from around the web:

Storage

Source: [H]ard|OCP

Intel SSD 525 Series Full Capacity Roundup - Intel Sweeps mSATA

Author:
Date: January 31, 2013
Subject: Storage
Manufacturer: Intel 525 Series Product Page
Tagged: Intel, ssd, 525, msata

Introduction, Specifications and Packaging

Introduction

It has been just under a year since Intel released their 520 Series SSD, which was their second 6 Gb/sec SATA unit. Sporting a SandForce controller, that release helped bridge a high speed storage gap in their product lineup. One year prior, Intel dabbled in the mSATA form factor, releasing a 310 Series model under that moniker. The 310 showed up here and there, but never really caught on as the physical interface was admittedly before its time. While in hindsight it was a very good way to go towards establishing a fixed standard, the industry had already begun fragmenting on these smaller interfaces. The MacBook Air had already launched with a longer 'GumStick' shaped SSD, and Ultrabook makers were following suit with units that were physically identical yet not pin-compatible with that used in the Apple product.

intel520.jpg

The Intel 520 Series SSD helped push Intel into 6Gb/sec SATA territory.

It's taken a while for the industry to favor defragmentation (pun intended) enough for mSATA to really start catching on, and that time appears to be nearing with Intel's launch of the SSD 525 Series:

525_FRONT_TILT_LEFT_300dpi.jpg

Read on for the full review!

Fit in three for the price of two with Icy Dock's SATA cage

Subject: Storage | January 24, 2013 - 06:41 PM |
Tagged: icy dock, MB153SP-B FatCage, sata 6Gps

Do you find yourself wishing you had more space to put in an additional three 3.5" HDDs and have nothing to do with a pair of 5.25" bays?  Icy Dock has a solution for you with the FatCage MB153SP-B which takes up two 5.25" bays and can fit three 3.5" SATA drives, even better it can run them with only two SATA power connectors.  Thanks to the easy opening front this might just be the easiest way to add hotswap drive to your machine without needing anything hanging off of the outside of your box.  As you can see from the rear shot, the drives are actively cooled and Pro-Clockers did indeed test the compatibility of 2.5" to 3.5" SSD adapters with no problems whatsoever.

PC_fatcage_19.jpg

"There are several manufacturers of such devices but we have one of the better ones on tap for you today. Icy Dock has been doing this for over fifteen years and has become a leader at it. FatCage MB153SP-B is one of several models coming from Icy Dock; the series would include the DataCage Basic and the FlexCage. Each having their own unique features, so we will try and get them into the lab so we can give you more insight on them."

Here are some more Storage reviews from around the web:

Storage

Source: Pro-Clockers

Intel's got a new SSD controller to show off to enterprises

Subject: Storage | January 17, 2013 - 03:05 PM |
Tagged: DC S3700, Intel, ssd, HET MLC, enterprise ssd

Before getting into the speed of the new Intel DC S3700 SSD, take a moment to consider the expected lifespan of the HET MLC flash, it was described to hardCOREware as "10 full drive writes per day over the 5-year life of the drive".  Now that will not have a big impact on home users, but Enterprise and image/video editors will certainly take note as moving that much data is a common occurrence for those businesses and the questionable lifespan of some flash memory has been contributed to the slow pace at which SSDs have been taken up by large businesses.  With the Intel name behind these drives, an assurance of long term usability and the impressive steady state performance they provide you may soon see these in a server room near you.

HCW intel-SSD-DC-S3700-800gb-disassembled.jpg

"The Intel SSD DC S3700 introduces a new Intel SSD controller for the first time in years. With a heavy emphasis on consistent performance, these drives bode well for the future of Intel SSD products. It may also refresh your opinion on some current SSDs that don't perform as consistently as others once they enter a steady state."

Here are some more Storage reviews from around the web:

Storage

Source: hardCOREware

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