Samsung SSD 850 Pro (128GB, 256GB & 1TB) Review: Enter the 3D Era
by Kristian Vättö on July 1, 2014 10:00 AM EST3D NAND: Hitting The Reset Button on Scaling
Now that we understand how 3D NAND works, it is time to see what it is all about. As we now know, the problem with 2D NAND is the shrinking cell size and the proximity of the cells, which results in degraded reliability and endurance. Basically, 3D NAND must solve these two issues but it must also remain scalable to be economical. So how does it do that? This is where the third dimension comes into play.
The cost of a semiconductor is proportional to the die size. If you shrink the die, you effectively get more dies from a single wafer, resulting in a lower cost per die. Alternatively you can add more functionality (i.e. transistors) to each die. In the case of NAND, that means you can build a higher capacity die while keeping the die size the same, which gives more gigabits per wafer and thus reducing cost. If you cannot shrink the die, then you have just hit a dead-end because the cost will not scale. That is what has happened with 2D NAND because the shrinks on X and Y axes have run out of gas.
What 3D NAND does is add a Z-axis to the game. Because it stacks cells vertically, it is no longer as dependent on the X and Y axes since the die size can be reduced by adding more layers. As a result, Samsung's V-NAND takes a more relaxed position on the X and Y axes by going back to a 40nm process node, which increases the cell size and leaves more room between individual cells, eliminating the major issues 2D NAND has. The high amount of layers compensates for the much larger process node, resulting in a die that is the same size and capacity as the state of the art 2D NAND dies but without the caveats.
The above graph gives some guidance as to how big each cell in V-NAND really is. On the next page, I will go through the method of how cell size is really calculated and how V-NAND compares with Micron’s 16nm NAND but the above gives a good picture of the benefit that 3D NAND has. Obviously, when each cell is larger and the distance between individual cells is higher, there are more electrons to play with (i.e. more room for voltage state changes) and the cell to cell interference decreases substantially. Those two are the main reasons why V-NAND is capable of achieving up to ten times the endurance of 2D NAND.
Moreover, scaling in vertical dimension does not have the same limitations as scaling in the X and Y axes do. Because the cost of a semiconductor is still mostly determined by the die area and not by the height, there is no need to cram cells very close to each other. As a result, there is very little interference between the cells even in the vertical direction. Also, the usage of high-K dielectrics means that the control gate does not have to wrap around the charge trap. The result is that there is a hefty barrier of silicon dioxide (which is an insulator) between each cell, which is far more insulating than the rather thin ONO layer in 2D NAND. Unfortunately, I do not know what is the exact distance between each cell in the vertical dimension but I think it is safe to assume that it is noticeably more than the ~20nm in 2D NAND since there is no need for aggressive vertical scaling.
As for how far Samsung believes their V-NAND can scale, their roadmap shows a 1Tbit die planned for 2017. That is very aggressive because it essentially implies that the die capacity will double every year (256Gbit next year, 512Gbit in 2016 and finally 1Tbit in 2017). The most interesting part is that Samsung is confident that they can do this simply by increasing the layer count, meaning that the process node will stay at 40nm.
Facebook
Twitter
RSS
160 Comments
View All Comments
GTVic - Tuesday, July 1, 2014 - link
Wondering if the 3D V-NAND has an effect on heat produced by each chip?Laststop311 - Wednesday, July 2, 2014 - link
If only this drive would of been a pci-e 3.0 x4 interface with nvme. We would of finally had a worthy upgrade. Yes it's performance is better than the 840 evo but you can get the 840 evo 1tb for 400 dollars even less if you catch it on sale. So you can get 2x 1tb 840 evo for almost the same price as 1 850 pro. If you compare an 840 evo with 25% OP to a regular 7% on the 850 the 840 evo looks just as good so 2x 825GB drives with 25% OP on each drive costs you 750-800 depending on the deal you get vs 700 for 1000GB. I would rather pay 800 for 1650GB than 700 for 1000GB with performance being nearly identical. I get an extra 650GB (which at 50 cents per GB is another 325 dollars worth of ssd) and tons of over provisioning to give the drive equal or better performance for only 100 dollars more (possibly less as the 840 evo has often sales)Sorry Samsung but 2x 1tb 840 evos with 25% provisioning gives me better or equal performance and a whole 650GB of extra storage for only 100 dollars more. At 50 cents per GB you get 325 dollars worth of more storage capacity for only 100 dollars more and thats with the 25% over provisioning which basically negates the performance increase of the new drives.
The only way samsung could of made this drive worth that money is if they had the drive on a pci-e 3.0 x4 interface with nvme instructions. I'm sure there will be tons of idiots who just buy it cause it's the latest drive. But if you use your brain you can see the 840 evo is still the best SATA drive when the cost/performance ratio is taken into account. 2x 1tb evo's in 25% OP mode gives you 1650GB and costs u 100 dollars extra or less and gives you the same performance or even better compared to 7% 850 pro 1000GB especially when raid 0 is taken into account. I'll take 1650GB over 1000GB if it's only 100 more and performance is equal or better easy choice.
Laststop311 - Wednesday, July 2, 2014 - link
Since samsung is stacking vertically now what they should of done is made a super huge 2tb drive to differentiate themselves from all these other drives. A 2tb drive for 1400 is a little more acceptable than 1tb for 700 simply because it's the only single drive with 2TB capacity.I can see great things happening with vertical stacked nand tho. When this process matures we should be seeing nand drives surpass spinning hard drives in capacity. When samsung has those 1tbit dies its planning for 2017 we should be able to have 8-12TB SSD's
althaz - Wednesday, July 2, 2014 - link
It's a new product and it's priced highly. Eager early adopters who want to move on to the latest and greatest will buy now, value-concious people will buy the 840s. Inventory of the 840s will get eaten up and the 850s will drop in price.This is what happens whenever any product is released, basically ever.
asmian - Wednesday, July 2, 2014 - link
Sorry, but neither this nor the EVO will get my money. Performance is all very well, even if only a tiny handful of users with extremely niche workloads will ever notice any difference, but all this extra reliability at a price premium means NOTHING without simple power loss protection. Restricting something so basic to "Enterprise" class products is the real gouging here by Samsung, not the price.If Crucial can provide that protection on the CHEAPEST drives in their class (M500/M550 and IIRC MX100 too) with performance that is not gimped as a balance, then there is no excuse for Samsung not to. This should be a no-compromise baseline for all SSDs going forward, and Anandtech should push hard for that - users should as well, by voting with their wallets and refusing to buy drives, however fast and powerful, that do not provide power loss protection as a basic feature.
bsd228 - Wednesday, July 2, 2014 - link
Though I agree it is a highly useful feature, it is far less significant to those of us using a good UPS. So I can't agree that it's a no compromise feature.romrunning - Wednesday, July 2, 2014 - link
What you aren't taking into account is the fact that the 850 Pro has MUCH higher endurance, and it's also more consistent. Those two items bring it more into the Intel DC 3500/3700 series type of class. It's not just a sheer performance comparison....and if you thing the 850 Pro is expensive, price out the larger Intel DC S3700 drives.
FunBunny2 - Wednesday, July 2, 2014 - link
"Real" Enterprise SSDs don't even have an MSRP. You negotiate with the vendor, and hope for the best. Now that Texas Memory is in IBM, and Fusion-io in SanDisk, with Violin likely to go somewhere. The conundrum is V.NAND's impact on flattening the curve between Enterprise and Commodity/Retail. At one time, a mainframe had bespoke 14" behemoth hard drive subsystems (in the case of IBM, run by the equivalent of a PDP-x). In due time, binned commodity 3.5" drives are now used.Samsung could well be the driving force to regularize solid state storage. The remaining issue is whether the file system hand waving will be dumped in favor of direct NVM persistence? Samsung, or whoever, likely couldn't care less.
romrunning - Wednesday, July 2, 2014 - link
It's been enjoyable to see a lot of "new" flash memory storage vendors pop-up. More competition is always good in that enterprise space.I've been looking forward to having more SSDs options available to servers at much better pricing. Solid storage advances have a trickle-down effect. If I can put an array of these Samsung 850 Pros into a server and achieve near "enterprise" performance, then that forces Dell/HP/etc. to drop their own SSD pricing.
watersb - Wednesday, July 2, 2014 - link
Fantastic detail of 3D NAND design and why it matters. Thanks very much!