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Everything You Need to Know About SLC, MLC, & TLC NAND Flash

Everything You Need to Know About SLC, MLC, & TLC NAND Flash
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Synopsis: This guide outlines the differences between SLC, MLC, and TLC NAND flash, explaining the pros and cons of each, to help readers choose the right SSD when upgrading.

Anyone who's tried one will attest, solid state drives (SSDs) sure are great! With faster load times for your favorite apps, higher overall efficiency, and added durability compared to traditional spinning hard drives, it's no wonder they're popping up in every new device that hits market.

But what makes certain SSDs more expensive than others? Like race cars, it's all about what's under the hood.


Quick Links


The Anatomy of an SSD

MyDigitalSSD BP4e mSATA SSD

MyDigitalSSD BP4e mSATA SSD with two enclosed NAND flash memory chips installed. The controller chip is designed by PHISON

  • A. NAND Flash: The part where your data is stored, in blocks of non-volatile (does not require power to maintain data) memory.
  • B. DDR Memory: Small amount of volatile memory (requires power to maintain data) used to cache information for future access. Not available on all SSDs.
  • C. Controller: Acts as the main connector between the NAND flash and your computer. The controller also contains the firmware that helps manage your SSD.

What is NAND Flash?

NAND flash memory is built up of many cells that holds bits, and those bits are either turned on or off through an electric charge. How those on/off cells are organized represents the data stored on the SSD. The number of bits in those cells also determine the naming of the flash, for example Single Level Cell (SLC) flash contains a single bit in each cell.

The reason behind SLC only being available at lower capacities is down to the physical real estate the NAND flash occupies on the Printed Circuit Board (PCB). Don't forget that the circuit board has to have the controller, DDR memory, and flash built to standard dimensions to fit inside your computer. MLC doubles the amount of bits per cell, whereas TLC triples, and this opens up for higher capacity SSDs.

There are particular reasons why manufactures build flash memory with a single bit per cell like SLC. SLC has the advantage of being the fastest, most durable but has the cons of being more expensive, and is not available in higher gigabyte storage capacity. That is why SLC is preferred for heavy enterprise usage.

MLC and TLC flash in comparison to SLC, is cheaper to produce, available in higher storage capacities, but at the tradeoff of relatively shorter life spans and slower read/write speeds. MLC and TLC are preferred for everyday consumer computer usage.

Understanding your own needs for computing and NAND flash basics will not only help you pick the right SSD, but will also help you figure out factors such as the price behind the product.


SLC (Single Level Cell)

The Single Level Cell flash is so called for it's single bit that can either be on or off when charged. This type of flash has the advantage of being the most accurate when reading and writing data, and also has the benefit of lasting the longest data read and write cycles. Program read/write life cycle is expected to be between 90,000 and 100,000. This type of flash has done exceptionally well in the enterprise market because of it's life span, accuracy and overall performance. You won't see too many home computers with this type of NAND due to its high cost and low storage capacities.

Pros:

  • Has the longest lifespan and charge cycles over any other type of flash.
  • More reliable smaller room for read/write error.
  • Can operate in a broader temperature range.

Cons:

  • The most expensive type of NAND flash on the market.
  • Often only available in smaller capacities.

Recommended for:

  • Industrial use and workloads that require heavy read/write cycles such as servers.

eMLC (Enterprise Multi Level Cell)

eMLC is MLC flash, but optimized for the enterprise sector and has better performance and lastability. Read/write data life cycles are expected between 20,000 and 30,000. eMLC provides a lower cost alternative to SLC, yet maintains some of the pros of SLC.

Pros:

  • Cheaper alternative than SLC for an enterprise SSD.
  • Has better performance and endurance over standard MLC.

Cons:

  • Does not match SLC NAND flash SSDs in performance.

Recommended for:

  • Industrial use and workloads that require heavy read/write cycles such as servers.

MLC (Multi Level Cell)

MLC flash as it's name suggests stores multi bits of data on one cell. The big advantage of this is the lower cost of manufacturing versus manufacturing SLC flash. The lower cost in flash production is generally passed onto you as the consumer, and for that reason is very popular among many brands. MLC flash is preferred for consumer SSDs for it's lower costs but the data read/write life is less in comparison to SLC at around 10,000 per cell.

Pros:

  • Lower production costs are passed onto you the consumer.
  • Is more reliable than TLC flash.

Cons:

  • Not as durable and reliable as SLC or enterprise SSDs.

Recommended for:

  • Everyday consumer use, gamers, and enthusiasts.

TLC (Triple Level Cell)

Storing 3 bits per cell, TLC flash is the cheapest form of flash to manufacture. The biggest disadvantage to this type of flash is that it is only suitable for consumer usage, and would not be able to meet the standards for industrial use. Read/write life cycles are considerably shorter at 3,000 to 5,000 cycles per cell.

Pros:

  • Cheapest to manufacture which in turn leads to cheaper to market SSDs.

Cons:

  • Cells will survive considerably less read/write cycles compared to MLC NAND. This means that TLC flash is good for consumer use only.

Recommended for:

  • Everyday consumer use, web/email machines, netbooks, and tablets.

The SSD Life Cycle

Like all good things, an SSD does not last forever. As noted above, a solid state drive's life cycle can be directly attributed to the NAND flash it comes with. SLC flash, for example, will last longer than MLC or TLC flash but that comes at a hefty price tag.

With MLC and TLC flash commonly used/found in consumer SSDs, the real question is how long will they last?

TechReport.com has tested several available consumer-grade SSDs, most of which were MLC NAND with one being TLC NAND, and the results are promising. All of the devices tested lasted at least 700 terabytes (TB) of writes before failing, and a couple even pushed passed a petabyte (PB).

This is a lot of data, but let's put that into perspective in writing 1 PB to an SSD.

1 petabyte (PB) = 1,000 terabytes (TB) / 1,000,000 gigabytes (GB) / 1,000,000,000 (MB)

That 1 PB could net you:

  • 222,222 movie DVDs at 4.5GB a DVD
  • 333,333,333 mp3 songs at 3MB a song
  • 500,000,000 jpg photos at 2MB an image
  • 15,384 installs of the game Grand Theft Auto V at 65GB an install

Looking at those numbers should really put to rest any doubts about your SSD failing in any short amount of time.

If you are considering an MLC or TLC SSD for everyday consumer use like; storing music, photos, software, personal documents or play games then you should feel assured that your SSD should last several years. This kind of usage is considered light compared to the ongoing heavy read/write usage of enterprise servers and computers as outlined in the next section below.

Note: For anyone worried about the lifespan of their SSD, features such as Self-Monitoring Analysis and Reporting Technology, or S.M.A.R.T. for short, can help you better keep track of your SSD's longevity.


Enterprise vs. Consumer SSDs

Enterprise SSDs are commonly found in database servers.

The difference and demands expected of enterprise SSDs set them a world a part from consumer SSDs. Enterprise SSDs are designed to meet a higher standard, and consistently perform in high-tech services, military, science and any area that would require a large amount of reading and writing data.

Database servers are an example of where you might see an enterprise SSDs, these servers are on 24/7 and that includes: longer read/write life cycle, faster read/write speeds, increased reliability and durability in harsh environments.

Consumer SSDs are less expensive, and are stripped down versions of enterprise SSDs. This may sound like you are missing out on certain features, but the benefits of a cheaper product with larger storage capacity are worth it. Besides manufactures are always increasing the performance of SSDs while bringing down the price.


In Conclusion

At this point, you probably have a good idea on the difference between SLC, MLC, and TLC NAND flash. The basics we discussed here, with insight into why some cost more than others, should clear up any confusion as to what type of flash best fits your needs.

Flash Type

SLC

Single Level Cell

eMLC

Enterprise
Multi-Level Cell

MLC

Multi-Level Cell

TLC

Triple-Level Cell

Read/Write Cycles 90,000-100,000 20,000-30,000 8,000-10,000 3,000-5,000
Bit Per Cell 1 2 2 3
Write Speed ★★★★★ ★★★★☆ ★★★☆☆ ★★☆☆☆
Endurance ★★★★★ ★★★★☆ ★★★☆☆ ★★☆☆☆
Cost ★★★★★ ★★★★☆ ★★★☆☆ ★★☆☆☆
Usage Industrial/Enterprise Industrial/Enterprise Consumer/Gaming Consumer

The important thing to take away from this guide is that modern SSDs are built to last a considerable amount of time. While their life-cycle should be taken into account, it should by no means prevent you from buying faster and more efficient storage.

Comments on Everything You Need to Know About SLC, MLC, & TLC NAND Flash

Skymax Monday, May 7, 2018 12:18:47 AM
What are disadvantages of ssd?
MyDigitalDiscount.com:
The common complaints about solid state drives are the limited storage capacity, compared to spinning hard drives, and the price per GB. That said, SSD prices have steadily dropped and will likely continue to as manufacturers release new flash innovations to raise capacities.
Vanni Sunday, May 6, 2018 11:01:09 AM
Dan Gendreau correction was in fact... wrong!
The original text was correct: a TLC cell can store 3 bits of data, that is EIGHT different voltage levels (source:
https://en.wikipedia.org/wiki/Multi-level_cell)
MyDigitalDiscount.com:
Thank you, the correction has been made. We'll be updating this post shortly to include QLC flash and adding more info to each section, clearing up any confusion for readers.
Gary Tuesday, April 17, 2018 09:50:12 PM
What about speed comparisons?
MyDigitalDiscount.com:
Speeds can vary based on a number of factors, notably the controller and firmware paired with the flash.
Dan Gendreau Tuesday, April 17, 2018 11:44:48 AM
Minor correction:
"TLC (Triple Level Cell) Storing 3 bits of data per cell"

This is Incorrect. Each TLC cell can store one of three possible STATES, not 3 bits. Think of each cell holding either a 0, a 1 or a 2. When combining multiple TLC cells, this works out to about 1.5 to 1.6 bits per cell on average.
MyDigitalDiscount.com:
Thanks for catching that! The change has been made.
Sam S. Saturday, December 23, 2017 11:00:52 AM
Very informative and transparent for all customers / consumers. Thank you for taking the time to make this available.
MyDigitalDiscount.com Tuesday, April 11, 2017 09:43:16 AM
Audrey,

Thank you, we are always looking at expanding on an ever changing technology.

If you are interested in being notified of further articles, please join us on Facebook here: facebook.com/MyDigitalDiscount
Audrey Monday, April 10, 2017 02:31:05 PM
Great article! Can you talk a bit about 2D and 3D MLC VS. 3D eTLC? Thanks!
MyDigitalDiscount.com Wednesday, April 5, 2017 11:06:00 AM
dragnr,

With any SSD purchase you should look at the warranty the manufacturer offers for their SSD with that type of flash. They will offer a limited warranty under years owned and/or TBW (Total Bytes Written). These numbers are not arbitrary, they do select them based on how they will maintain optimal performance under regular use.

Other factors like firmware and daily use can impact the long term SSD performance.

For average gaming under MLC flash you should be fine under warranty

MyDigitalDiscount.com stocks a variety of MLC flash based SSDs here http://tinyurl.com/mvfaxp8
dragnr Wednesday, April 5, 2017 05:16:29 AM
very nice and good article, only thing I want to know is how long is that cycles means in term of years, for example the MLC read/write cycles is 8000-10000, so how many years will it last? lets say average gaming usage? thanks.
MyDigitalDiscount.com Friday, January 6, 2017 08:37:59 AM
Frank,

We have not encountered an eSLC as of yet. SLC flash on its own is a high-grade flash, and low capacity aside is more than suitable for enterprise applications


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