Samsung SSD 850 PRO 256GB - A Game Changer in the Making

The Benefits of Your Own Foundry

Vertical integration, that is the keyword today in the SSD business. In an increasingly competitive and crowded marketplace, it is important to be able to distinguish yourself from your competitors and being vertically integrated, meaning to have your own NAND foundry, memory controller and firmware, allows a brand to have control over prices, performance and reliability - three key factors that can make or break a drive.

Strictly speaking, the only true vertically integrated SSD manufacturers in the market today are Samsung and OCZ/Toshiba - Toshiba already has its own TC358790XBG controller, but with the acquisition of OCZ gains the latter’s excellent Indilinx Barefoot 3 controller. The other key players such as Crucial, Intel and SanDisk come close as they have their own NAND foundries, but they still rely on third-party memory controllers. Seagate could well be an important player in the future as they have acquired LSI's flash businesses from Avago, the people behind SandForce, but still lack the capability of producing their own NAND chips.

As a result of being vertically integrated, we were not surprised to hear that in the middle of last year, Samsung was embarking on brand new type of NAND memory called 3D Vertical NAND (3D V-NAND) to overcome the shortcomings of traditional MLC (2-bit per cell) and TLC (3-bit per cell) NAND. What are these shortcomings? We have written about it at length in our review of the Samsung SSD 840 EVO, but let us go through it again as it is important to our appreciation of 3D V-NAND.

Shortcomings of Traditional NAND

In a bid to make SSDs more affordable and accessible, one of the important things for SSD manufacturers to do was to increase memory density. There are two ways to achieve this: use smaller manufacturing processes or increase the number of bits per cell. For Samsung, they chose the latter and are still the only SSD manufacturer to offer drives that use TLC NAND (Triple-Level-Cell). Data is stored in NAND by manipulating voltage stages and with TLC NAND, you get eight voltage stages per cell - four voltage stages in MLC NAND and just two in SLC NAND. What this means is that more dies can be harvested from a single wafer, thus reducing overall manufacturing costs.

However, there are two key downsides to this approach and they are performance and endurance. With eight voltage states to check, random reads will take more time - roughly twice as long as MLC NAND (theoretically speaking). Endurance is affected because having additional voltage stages reduces the margin between the individual stages, and this is crucial because as you write to the cell, the layer of silicon oxide that acts as an insulator gradually wears out. When it does, higher voltages will be needed to program the cell to one of its eight states, which further reduces the margin between them. Gradually, the margin will be so small that the cell can no longer be effectively used and has to be retired. Therefore, while MLC NAND SSDs are typically good for 3000 P/E (program-erase) cycles, expect TLC NAND SSDs to enjoy less, perhaps as little as 1000.

On the other hand, using small manufacturing processes has it own set of issues. To put it plainly, reducing the manufacturing process means squeezing more cells onto the die, which in turn means there is less space between each cell. And since each cell has to hold a charge, the interference from neighboring cells can sometimes disrupt or even inadvertently change the state of the cell that is next to it and cause the data to become corrupt.

Enter 3D V-NAND & The Samsung SSD 850 PRO

If you really think about, so far, the industry’s attitude towards increasing memory density has been to solve the problem on a two-dimensional plane - squeeze more cells into a fixed area or increase the number of bits per cell. While it has gotten us far, the fact is that we have reached a point where a radical shift in technology is required if NAND memory is to be a viable form of storage in the future.

Fortunately, Samsung has come up with an elegant solution to the industry’s current predicament and that is to stack the cells on top of each, hence the name 3D Vertical NAND. And because the cells are now stacked on top of each other, there is more 'space' so to speak and therefore there is no need for the cells to be cramped so closely together. As a result, Samsung can 'go back' to a more manageable process node of 40nm. This in turn helps improve performance and endurance. Apart from improved performance and endurance, Samsung also said that such NAND will also be easier to program and will therefore require simpler algorithms and firmware. This not only boosts performance further, but also means 3D V-NAND will be more power efficient (remember earlier that cells are programmed by changing their voltage states). 

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When we first reported on Samsung’s use of 3D V-NAND, the company was only experimenting with NAND that had 24 layers of stacked cells. These NAND with 24 layers of stacked cells are now used in Samsung’s enterprise SSDs. Now, almost a full year on, Samsung has improved on its technology to offer NAND with 32 layers of stacked cells. And it is this second-generation of 3D V-NAND that we see being employed in their latest flagship consumer SSD, the SSD 850 PRO, which was first announced at Samsung's Global SSD Summit just last week.

Apart from 3D V-NAND, very little else has actually changed in the new SSD 850 PRO. The drive does not feature a brand new controller and instead uses the same 3-core MEX controller that was also used in the SSD 840 EVO. It also uses the aging SATA 6Gbps interface. And like the rest of Samsung’s offerings, the SSD 850 PRO will offer full disk 256-bit AES encryption. However, Samsung’s very effective RAPID mode technology has been tweaked such that it can now use up to 2GB of system memory for its caching.

Test Setup

The drives will be tested on our recently revamped storage testbed. The main changes are the faster Core i5-2500K processor and an accompanying Z77 motherboard which has native Thunderbolt connectivity.

• Intel Core i5-2500K (3.3GHz)
• ASUS P8Z77 Pro Thunderbolt (Intel Z77 chipset)
• 2 x 2GB DDR3-1600 memory
• MSI GeForce 8600 GTS
• Windows 7

We have also revised our benchmarks, ditching older benchmarks such as HD Tune and also including an all new timing test to better evaluate the drive’s real world performance. The list of benchmarks used are as follows:

1. AS-SSD benchmark 1.7.4739
2. CrystalDiskMark 3.0.1
3. PCMark 7 (Storage suite)
4. Iometer (version 2006.07.27)
5. Timing Tests (Cold start, Reboot, Apps Launching)

The Samsung SSD 850 PRO will be closely pitted against its predecessor, the SSD 840 Pro, which also happens to be the winner of our last Great High-end SSD Shootout. We are also comparing it against other SSDs from top tier brands with their own memory controller or NAND foundry, such as the Plextor M5 Pro Xtreme, OCZ Vector 150, SanDisk Extreme II and the Toshiba Q-Series. Here are the full list of drives tested:

• Samsung SSD 850 PRO
• Samsung SSD 840 PRO
• Samsung SSD 840 EVO
• Plextor M5 Pro Xtreme
• OCZ Vector 150
• Sandisk Extreme II
• Toshiba Q-Series

Timing Tests

Recently added to our evaluation of SSDs is how they perform in real world everyday situations, namely booting up from a cold start, reboot and launching applications. As for the applications used, we made the drives launch 11 applications from the Adobe CS6 suite of utilities simultaneously, which includes resource intensive applications such as Photoshop, InDesign, Dreamweaver, Premiere Pro amongst others. As a point of reference, a 7200rpm mechanical hard disk would take over 5 minutes to open all the applications.

The new SSD 850 PRO got off to a promising start and it was about on a par with the older SSD 840 PRO. It was the fastest drive to boot from a cold start and also the quickest to reboot. The time it took to launch the entire Adobe CS6 suite of apps was also very competitive at 11.4 seconds - just a tenth of a second slower than the SSD 840 PRO. All in all, its timings were amongst the lowest we have recorded.

CrystalDiskMark 3.0.1 Results

CrystalDiskMark is an easy-to-run and quick utility to use to gauge a drive’s performance. It measures sequential read and write performance and random read and write speeds of random 4KB, 4KB (queue depth 32) and 512KB data.

The older SSD 840 PRO was a stellar performer on CrystalDiskMark and the new SSD 850 PRO did not disappoint. Overall, the SSD 850 PRO’s performance was very close and similar to the SSD 840 PRO. But this is not necessarily a bad thing as the SSD 840 PRO was the top performer on this benchmark. If anything, it just goes to show how adept the SSD 840 PRO was and that the SATA 6Gbps interface is fast becoming the limiting factor when it comes to SSD performance. 

AS SSD 1.7.4739 Results

AS SSD is a benchmark that uses non-compressible and completely random data. What this means is that the drives using the SandForce SF-2281 controller cannot compress the data first, which takes away one of the strong advantages of this controller. Therefore this is a useful benchmark because drives that use the SF-2281 controller or similar, don't gain an upper hand.

On AS SSD, the new SSD 850 PRO exhibited appreciably higher copying speeds than its predecessor on the Copy Benchmark. However, the top performer here was still Toshiba’s Q-Series SSD. Moving on, we noted that it recorded very high sequential read and write speeds that were in line with Samsung’s older SSD 840 PRO and EVO drives. 4k read and write performance was also very similar, but noticeable gains were recorded on the intensive 4k, 64 queue depth workload. Here, the SSD 850 PRO managed read speeds of around 386MB/s, the highest recorded and an improvement of over 14% over the older SSD 840 PRO. Write speeds were also very high and loses out only slightly to the OCZ Vector 150. Overall, however, the SSD 850 PRO was easily the best performing drive on this benchmark.

PCMark 7 Results

PCMark 7 is a benchmarking suite from FutureMark that evaluates the performance of Windows 7 machines. It tests a wide range workloads and aspects of the system ranging from computation, image and video manipulation and storage. We’ll be looking solely at the storage test here.

The SSD 850 PRO managed a PCMark score of 5622, although this is the highest amongst the drives tested, it is just seven more than the SSD 840 PRO. However, if we were to look at the breakdown, we can see that it is marginally faster across all workloads, losing out only on the “Starting Applications” work scenario. This consistency in performance is quite impressive.

Iometer Results (Part 1)

Lastly, we put the drives through the rigorous grind of Iometer, with different workloads and I/O queue depths. We have chosen to show results from a queue depth of 1 to 5 as this better represents the workloads a typical consumer might face.

The SSD 850 PRO’s streaming read and write performance was stellar and amongst the highest we have recorded. Compared to its predecessor, streaming write performance has improved noticeably as we approached higher queue depths. However, it was on the File Server workload that we saw the greatest improvement. The SSD 850 PRO’s showing on the Web Server workload was impressive too as it slightly outclassed the SSD 840 PRO. Overall, the SSD 850 PRO is easily the top performer again.

Iometer Results (Part 2)

Finally, we look at the I/O response times for the workloads reported on the previous page. Given the SSD 850 PRO’s impressive results on the previous page, it is only logical to see that it also recorded the lowest average response times.

Greatness Awaits

Despite the multitudes of different SSDs that are available in the market today, truly great innovations in this market are few and far between. The reason for this is because there are only a handful of NAND manufacturers and an equally small number of choices when it comes to memory controllers. The last time we were so excited about a drive was possibly the time OCZ released its Vector SSD, which featured its own in-house developed Indilinx Barefoot 3 controller.

Although the new SSD 850 PRO does not have a brand new controller, what it does have is a all-new type of NAND memory and it is truly groundbreaking. More important, however, is what the future might hold. According to Samsung, they are only scratching the surface of just what is possible with 3D V-NAND and one way for it to increase densities even further is to stack more layers. Right now, the SSD 850 PRO uses 3D V-NAND that has 32 stacked layers of cells and in theory there is no real limit to how many layers this can go. 32 layers might sound like a lot, but really, when the cells are this small, it does not make the NAND packages any thicker. And while Samsung has said that there is no limit to how many layers it can stack, what we think they really mean is that there is no limit for the foreseeable future. As more and more layers are stacked upon each other, interference will likely rear its ugly head once more, but for now at least, it is all good and this technology is still highly scalable.

Alternatively, Samsung can also apply its TLC NAND technology to its 3D V-NAND. Right now, the Samsung SSD 850 PRO utilizes MLC 3D V-NAND that stores only two bits of data per cell. In anycase, Samsung’s projections for 3D V-NAND is that it will eventually produce NAND that offers 1 Terabit of capacity per die. Right now, the Samsung SSD 850 PRO uses 3D V-NAND that is produced at using a 40nm process node that gives it an overall memory density of 86Gbit per NAND die. Hard disk manufacturers who have long been confident that mechanical hard disk drives will continue to beat flash drives in terms of capacity should definitely sit up and start taking notes.

Back to the SSD 850 PRO and it is obvious and apparent that it is the most well rounded SSD that we have tested. Performance is top notch and highly similar to that of the older SSD 840 PRO but with notable improvements in a few areas- notably on the File Server workload on Iometer, which used to be the SSD 840 PRO’s only failing. However, while the SSD 850 PRO is the fastest SSD we have ever tested, its performance is proof that the aging SATA 6Gbps is the limiting factor.

But while performance might not be as great as expected due to the limitations of the SATA interface, endurance is greatly improved so much so that Samsung says it will survive at least 150TB of writes and is offering 10-year warranties on all models of the Samsung SSD 850 PRO - even the 128GB model. To put this number into some context, this means that even if you write 50GB to it daily, it will last 8 years. 50GB write workloads are actually very high and most mainstream users typically only write 10GB to 30GB to their drives each day. Hence, if we were to use a middle ground figure of 20GB, we are looking at a drive lifespan of over 20 years. Remember also that endurance scales linearly as we go up capacity points, so the 1TB version of the Samsung SSD 850 PRO could very likely outlive you. Here’s a table of the SSD 850 PRO’s project lifespan that Anandtech has calculated using different parameters. If you like to read up on their calculations in detail, you can hit this link here. But to put it very briefly, endurance should not be a concern for users.

Sadly, as with all things in life, you cannot have your cake and eat it and so it should come as no surprise that the SSD 850 PRO will come with a high price tag. Samsung has not fixed a date yet on local availability and we were only told that it should be available from Q3 onwards. As for price, the 256GB version reviewed here will have a recommended retail price of S$329, which makes it one of the priciest drive in at this capacity point and also around S$60 more than the older SSD 840 PRO.

For those looking for a small capacity drive to house only their OS and commonly used applications, the 128GB is not much cheaper and comes in at S$228, making it the only drive at this capacity point to go above the S$200 mark. The 512GB and 1TB variants are equally pricey, costing S$649 and S$1,009 respectively. As a point of comparison, a 1TB Samsung SSD 840 EVO is currently retailing at S$699. Here’s a breakdown of the cost per gigabyte of the various Samsung drives.

In closing, the SSD 850 PRO is an awesome drive that offers tons of performance and bucket loads of endurance. And while the price may be high, we think it is well justified considering what it offers. Unfortunately, it seems that it is being held back by the limitations of the aging SATA interface. That said, the SSD 850 PRO is well worth your consideration if you looking to get your first SSD or if you are upgrading from a much older model. For users who are already using an SSD 840 PRO, the performance gains will probably be negligible. Nonetheless, the SSD 840 PRO is still a top, top drive.

For those who can afford to wait or have the intention to upgrade to Intel’s new 9 Series chipset, Samsung has also told us that a M.2 variant will likely be made available in early Q4 of this year, while a PCIe variant is likely to debut early next year. With the increased bandwidth offered by the M.2 and PCIe interfaces, these drives will likely be blazing fast and we can't wait to get our hands on them.

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