Understanding TLC NAND
by Kristian Vättö on February 23, 2012 1:14 PM EST- Posted in
- Storage
- SSDs
- OCZ
- Indilinx Everest
- TLC
Availability and Controller support
Just to make this clear, TLC isn't anything new. For example Hynix had a 32Gb 48nm TLC die in 2008. This is because TLC was originally used for devices like USB flash drives, where its poor endurance would be negligible. Most SSD OEMs have been toying with TLC SSDs for at least a year now but we haven't seen any commercial products. OCZ had originally planned to introduce its first TLC based SSD in the Q1 2012, however TLC pricing simply hasn't made sense yet. Unless OCZ can leverage a significant cost savings over 2-bit-per-cell MLC, the added headaches of bringing a lower performing TLC part to market don't make sense.
However there's still significant motivation to migrate towards TLC NAND. Further bringing down costs, particularly for consumer SSDs aimed at light, particularly read heavy workloads makes a lot of sense. Increasing pressure from Intel to deliver cheaper SSD enabled Ultrabooks, and Apple's desire to move all mainstream Macs to solid state storage are two major motivations. MLC NAND pricing will eventually get low enough to meet these (and more) needs, but TLC definitely accelerates the process.
TLC does require controller and firmware support. In the client SSD space only OCZ has been aggressive with announcing that its Indilinx Everest controller supports 3-bit-per-cell NAND.
Adding controller support for an extra bit per cell is more than just updating the datasheet and claiming it works. The ECC engine needs to be updated as the controller will face more frequent and more severe errors with TLC NAND (and its associated lower endurance rating).
Maintaining low write amplification is even more important with TLC NAND. With significantly fewer available program/erase cycles, burning through them due to high write amplification isn't acceptible. While NAND endurance isn't really an issue for most client MLC drives, it may be an issue for TLC based drives.
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Kristian Vättö - Friday, February 24, 2012 - link
There is HET-MLC (or usually known as eMLC) which is MLC NAND aimed for enterprises. It stores two bits per cell like normal MLC but its P/E cycle rate is much higher (IIRC something like 50,000). Unfortunately I don't know how it really differs from regular MLC but it's a lot more expensive than regular MLC.SLC, MLC and TLC simply refer to the amount of bits per cell, there is no 1-bit-per-cell MLC as MLC alone means multi-level-cell, and one isn't multi ;-)
ckryan - Friday, February 24, 2012 - link
I wasn't aware that this was going on until I read the UCSD paper "the Bleak Future of NAND Flash Memory. Somehow, you can use MLC to store just one bit, and it gets similar, but not identical, performance to SLC.http://cseweb.ucsd.edu/users/swanson/papers/FAST20...
This was the study that was said to cast doubt on the ability to scale NAND effectively past 2024.
They tested this particular MLC-1 setup. Even if you discard half the capacity of MLC, it's still cheaper than SLC bit for bit.
HET-MLC and eMLC really are just highly binned MLC NAND. Toshiba gives it's eMLC 10kPE cycles. But enterprise drives only have to retain data for 3 months at MWI=0, so some of this extra endurance comes from that.
Kristian Vättö - Friday, February 24, 2012 - link
Ooh, interesting, thanks for the link! I was sure that you had mixed up eMLC and MLC because MLC-1 doesn't make much sense, at least not without further explanation.Does the study say how much cheaper MLC-1 is when compared with SLC (I don't have time to read it thoroughly now, but will do tomorrow)? Like I said in the article, MLC is the highest volume product and gets the new process nodes first, so that might be the reason why MLC-1 is a bit cheaper than SLC. Shouldn't be much, though.
This Guy - Friday, February 24, 2012 - link
There is a better tech in the wings anyway. Memristors:http://www.electronicsweekly.com/Articles/06/10/20...
Memristors will create a giant performance boost. Their low latency and high density will allow for the replacement of HDDs and RAM. And this could be a second generation product out in three years.
If the worst memory latency was ~20ns instead of ~50µs (SSD) or ~20ms(HDD), cache misses would stop being a problem. Old, simple CPU architectures could be reproduced (with I/O upgrades) and bundled with memristor storage and compete with current designs.
In 10 years we could see CPUs replaced with multi-chip modules containing large memristor banks, ALU's with a far larger variety of operations (including GPGPU operations) and the system's I/O. No cache. No registers. No stalls.
jjj - Saturday, February 25, 2012 - link
Those are dreams for now.Anyway Sandisk/Toshiba sell a lot of TLC already, in certain products.They even had 4 bits per cell but that's not being produced anymore.As for the future they got 2 things, BiCS and 3D ReRAM. We'll see soon enough if any of those make it to market .
rpmurray - Thursday, February 23, 2012 - link
While cheaper is sure tempting I'm not making the move until I stop seeing so many users giving one-star ratings on Newegg when their nice new SSD bricks itself anywhere between one day and three months.jdjbuffalo - Thursday, February 23, 2012 - link
As opposed to all the people who get new 2TB hard drives that fail in the first day?pc_void - Thursday, February 23, 2012 - link
So true. It is said that if it lasts for 3 months then it will probably last for years - talking about hard disk drives or anything for that matter.In my opinion, people brick ssd drives because they are not dummy proof.
pc_void - Thursday, February 23, 2012 - link
Except for the exceptions.Folterknecht - Thursday, February 23, 2012 - link
The same goes for many other components - hdds, gpu, mobo ...And often enough there is either a crappy PSU or RAM involved doesnt work as it should. I dont really trust those "user reviews" on sites like Newegg, to many people writing there that have no idea what they are talking about.
Of course firmware issues exist, not denying that, but thats no reason pass the best possible upgrade for your pc (in most cases).