Samsung SSD 840 (250GB) Review
by Kristian Vättö on October 8, 2012 12:14 PM EST- Posted in
- Storage
- SSDs
- Samsung
- TLC
- Samsung SSD 840
A TLC Refresher
Back in February, we published an article called Understanding TLC NAND, where we went in-depth about how NAND works and the differences between various kinds of NAND (SLC, MLC, and TLC). Back then we didn't know when TLC SSDs would be publicly available or who would be the first manufacturer. Supposedly, OCZ had interest in releasing TLC based SSDs but the supply of TLC NAND wasn't good enough for their needs. Samsung has the benefit of being a tier one manufacturer that makes its own NAND, which gives it an advantage when dealing with new technologies as it can control the output of NAND. In this case, Samsung was able to ramp up the production of TLC NAND when it wanted to, whereas OCZ must live with whatever the NAND manufacturers are ready to sell them.
While we have covered TLC in detail already, we have some new details to add:
| SLC | MLC | TLC | |
| Bits per Cell | 1 | 2 | 3 |
| P/E Cycles | 100,000 | 3,000 | 1,000 |
| Read Time | 25us | 50us | ~75us |
| Program Time | 200-300us | 600-900us | ~900-1350us |
| Erase Time | 1.5-2ms | 3ms | ~4.5ms |
Samsung would not tell us the exact read, program, and erase latencies but they told us that their TLC is around 50% slower than their MLC NAND. We don't know the latencies for Samsung's MLC NAND either, hence we have to go by general MLC NAND latencies, which varies a lot depending on process. However, we were able to get the P/E cycle count for TLC, which is 1,000. Samsung did not specify the process node but given that they listed MLC at 3,000 cycles, we are most likely talking about 27nm or 21nm. I wouldn't find it unlikely that Samsung is rating their 21nm MLC NAND at 3,000 P/E cycles as well because IMFT was able to keep the endurance at the same level with their 20nm MLC NAND.
Physically, TLC is similar to SLC and MLC. All three consist of similar transistors, the only difference is that they store a different amount of bits per cell. SLC only stores one, whereas MLC stores two and TLC stores three. This actually creates a minor problem, as there is no multiple of three that is a power of two. Unlike with hard drives, SSD capacities typically go in powers of two, such as 64GB, 128GB, and 256GB.
NAND is actually built based on binary prefixes (Mebi, Gibi...) but is almost always referred to using metric prefixes (Mega, Giga...). For example a 128GB SSD has ~137.4GB of storage (128GiB) due to Gibi to Giga translation, but the remaining space is used as spare area.
If the raw NAND array has 17.2 billion transistors, you would get 16Gibibits (17.2Gbits) of storage with SLC NAND because each cell can store one bit of data. MLC yields 32Gib, which is still a nice power of two because all you're doing is adding one level. However, with TLC you get 48Gib, which is not a power of two. Technically nothing is stopping manufacturers from making a 48Gib die, but from the marketing and engineering standpoint it's much easier to stick with powers of two. A TLC die in this case should be 32Gib just like MLC. To achieve that, the die is simply reduced in size to around 11.5 billion transistors. 32Gib isn't exactly divisible by three, but thanks to spare bits it doesn't have to be. The trick here is that the same capacity TLC die is smaller than an MLC die, which results in more dies per wafer and hence lower production costs.
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mayankleoboy1 - Monday, October 8, 2012 - link
Samsung is known to release only a few firmware updates (unlike SF).But due to the somewhat quirky nature of TLC NAND, do you expect Samsung to release a newer firmware , with maybe better read performance , or better TRIM support ?
Taft12 - Monday, October 8, 2012 - link
Who cares?? Frequent firmware updates are a sign of an incompetent engineering and testing. I'll stick with the vendors known for getting it right the first time thank you very much.JuneBugKiller - Monday, October 8, 2012 - link
If Samsung 840 120GB cost's $109.99 and you can get an OCZ Vertex 4 128GB for $104.99, which is faster in 80% of the benchmarks and is $5 cheaper then who's going to want it? So what if the price goes down to $80, are people going to save $25 thinking their hard drive is going to die twice as fast. I have bought (with works money) around 30 ssd's including Intel 80GB & 160GB Silver Case, Intel 710 100GB, Vertex 3 Max IOPS 120GB and Vertex 4 128. So far I've only had 2 ssd's go bad and they were both Intel 80GB ssd's. One wouldn't power on and the other reported at 8MB. Intel replaced them under warranty.The point is I have been buying SSD's for years and I just don't see how anyone would want these samsung ssd's. Samsung is famous for huge margins on each product. When a company pockets $240 off of a $500 tablet and their name isn't Apple then something is wrong.
JarredWalton - Monday, October 8, 2012 - link
Wow, talk about skewing the data by cherry picking the worst-case numbers for the 840. The Vertex 4 is only 85% faster in one specific test: AS-SSD Write performance. Of course, in the AS-SSD Read performance it's also 10% faster than the Vertex 4 256GB, but you just ignore that? Samsung also has some of the best SSDs in terms of large reliability figures, so even if the 840 is slightly slower than other drives in some tests, it may be the better option. Also don't forget to factor in that the 840 appears to be well-tuned for light workloads (e.g it's near the top of our light workload results).Personally, I think the 840 needs to come in below the current 830 drive prices to make sense, and it probably will not long after the official release. 128GB 830 drives already go for under $100, and 256GB drives have been at $200 for over a month now -- likely all in preparation for the release of the 840. TLC NAND is cheaper to manufacture (per GB), and long-term it will be significantly more profitable for Samsung. Get some good DSPs added into the mix and I wouldn't be surprised to see most SSDs in two generations being TLC based, with MLC moving to the enterprise level and SLC basically going away because it's too expensive.
JuneBugKiller - Monday, October 8, 2012 - link
No I'm talking about counting each benchmark add the total and divide the number by how many OCZ Vertex 4 won and it was over 80% of the total number of benchmarks. How is Samsung a better option? TLC over MLC, OCZ fastest drive to Samsungs slowest new drive. Of course Samsung is going to make more profit but why would you want to spend the same amount on a slower drive with less endurance?JarredWalton - Monday, October 8, 2012 - link
Sorry, 80% of benchmarks is correct; I read that wrong. But let's put that in perspective:http://www.anandtech.com/bench/Product/678?vs=628
If we look at average performance across all benchmarks, the difference between OCZ Vertex 256GB and Samsung 840 250GB is a 12.4% advantage for OCZ. However, OCZ hasn't exactly been free from firmware issues. That right there is the reason many people will pay a bit more for a Samsung (even if it's slower).
Would I buy an 840 right now for $200 or whatever? Definitely not -- I'd actually take the 830, just for proven reliability over time. Give the 840 a couple months just to be safe, then check the prices. If it's still more expensive than the Vertex 4, sure, go for OCZ if you'd like. If they're the same price, though, the 12% performance is practically meaningless for most consumer workloads.
sean.crees - Monday, October 8, 2012 - link
Because it's not just about performance, it's also about reliability. This is user data we are talking about. Even a single loss could be catastrophic. OCZ doesn't have the reliability track record that Samsung and Intel has, and for that reason there are many people who will only ever buy from Samsung or Intel. So then OCZ isn't even mentionable. It doesn't matter if they are faster because who cares if your data is at risk?Also you have to consider that the REAL WORLD difference between any modern 6Gbps SSD is negligible, so then performance means even less. It ends up being a contest of reliability instead of a contest of speed. In that contest, OCZ loses.
krumme - Monday, October 8, 2012 - link
I would want it :)We have about 7-8 ssd in the house, about 3 of those is vertex 3 ssd, and there have been realiability and firmware issues.
I think ssd speeds since the last 2 years have been good enough and would prioritize reliability any day.
I had to replace an sandisk u100 in my Samsung 9 series x3c to a faster one, but that was because the u100 was like a return to 4 years ago. Its a good backup now.
Now hopefully reliability is there, and prices will go down so everyone can afford it. We dont need more firmware updates and shit. Its like the first 3d gfx in the mid 90, - a mess.
But you are right Samsung is starting to get expensive, and charge for the brand. Wether you like it or not it will certainly mean more Samsung reviews too. Being a big boy, have advantages :)
Taft12 - Monday, October 8, 2012 - link
"If Samsung 840 120GB cost's $109.99 and you can get an OCZ Vertex 4 128GB for $104.99, which is faster in 80% of the benchmarks and is $5 cheaper then who's going to want it?"A person who values reliability at a value higher than $0 will choose the non-OCZ product every time.
Jaybus - Thursday, October 11, 2012 - link
Time will tell. The TLC NAND should end up around 30% cheaper per GB than MLC. Then it will come down to buying a 240 GB MLC for $200 or a 320 GB TLC for the same price.