by Ilya Gavrichenkov
06/07/2013 | 04:02 AM
When SSD makers want to emphasize their advantages, they often talk about how much engineering resources they put into their products. A typical SSD has three basic constituents: flash memory, controller and firmware. Not all of the firms engaged into SSD business today create these components on their own. On the contrary, the majority of consumer-class SSDs are assembled out of parts manufactured by third parties as if from Lego bricks.
So if we want to rank SSD makers according to how original their products are, we have to start from the SandForce platform. Most of SandForce-based SSDs are merely clones of the reference design that use flash memory from Intel or Toshiba and reference firmware from LSI.
The next tier consists of companies that do not develop and do not manufacture semiconductor components but try to offer original products by means of software optimizations and customized firmware. For example, Corsair and Plextor (Lite-On) assemble SSDs out of popular flash memory types and widespread controllers but deliver products that have no analogs.
Of course, it’s even better to have one’s own flash memory manufacture. Intel, SanDisk and Crucial (Micron) always have some of their own chips in their SSDs, which helps them apply a more flexible pricing policy.
Having one’s own SSD controller is the dream of any SSD maker, though. Developing one calls for some serious engineering resources, but the end result is likely to be superior to competing solutions because any user requirements can be accounted for in this case. OCZ is an example of the company that has its own SSD controller, but it doesn’t manufacture semiconductor components.
Therefore, it is not OCZ but Samsung that takes the top place in our rating. Samsung can build SSDs consisting of 100% Samsung components: an original controller with original firmware and Samsung-made flash memory. Although this doesn’t guarantee success, Samsung does have everything necessary to deliver high-performance, reliable and inexpensive SSDs that many end-users dream of.
That’s why it is with high hopes that we test Samsung SSDs. The previous 830 series had very attractive specifications and was actually among the best for a long time. Later on, the company improved its controller and began to make faster and cheaper flash memory, which resulted in the new and highly promising 840 series. It comes in basic and professional versions, and we have an opportunity to check out both of them today.
Being a major manufacturer of NAND flash, Samsung can easily introduce cutting-edge memory types into its serially produced SSDs. The new 840 series is a good example as both the basic and Pro versions boast 21nm flash with Toggle Mode 2.0 interface whose bandwidth has been increased up to 400 Mbit/s. That’s not the key feature of Samsung's new products, though. Their main advantage is the fourth-generation MDX controller. Samsung has been improving its controller noticeably with each new SSD series, so the chip employed in the 840 series aspires to be the fastest consumer-class SSD controller available right now.
It is based on three 300MHz ARM Cortex-R4 cores. Besides a faster version of the ARM architecture, the controller offers a 40% advantage in clock rate in comparison with its predecessor from the Samsung 830 series. The previous MCX controller could hardly be blamed for low performance and the new MDX has even better computing resources, which is important in terms of Samsung's declared priorities. When developing the new products, the company focused on making them faster at processing random-address data. This kind of load is typical of a lot of everyday tasks and today's SSDs are not as good at handling it as they are at sequential reading and writing.
To process a lot of unrelated I/O requests the SSD controller must translate LBA addresses used by the OS into the actual position of data in the flash memory. It is here that today’s SSDs may improve yet. The speed of processing random-address data blocks is much lower than the SATA 3 bandwidth, so Samsung focused on increasing it. This is indicated by the specified characteristics of the new SSDs we can compare with the specs of the older Samsung 830:
The manufacturer promises a 25% increase in random read speed whereas random writing may be up to 2.5 times as fast as before. That’s impressive, we must admit. Featuring faster memory and no artificial bottlenecks, the Samsung 840 Pro is expected to deliver the highest performance, so we are going to start with it.
Our sample of the Samsung 840 Pro was packed into a small and stylishly designed cardboard box painted mostly black. The storage capacity is indicated by a sticker on the front of the box. The product’s key features and specifications are listed on the back.
The SSD is fixed in a plastic wrap along with its accessories which do not include a 2.5->3.5-inch system case adapter. There are just a few documents, a couple of stickers and a CD with electronic manual and software.
The SSD itself looks gorgeous. Made out of aluminum alloy, it is black-anodized and has shiny fascias on its face side. A manufacturer logo and terracotta square are painted on the top of the case, so you can easily identify the 840 series. On the bottom of the case there is a dark-gray sticker with full product name, part number, barcodes and serial number.
The case is 7 mm thick and Samsung doesn’t offer any frames or faceplates to increase its thickness to the more conventional 9.5 mm.
The PCB is populated on one side only. All of the chips we can see on it are manufactured by Samsung itself.
There are three kinds of chips in this SSD. First, it is the above-described Samsung MDX controller. Second, there is a low-voltage LPDDR2-1066 SDRAM chip for 512 MB of cache memory. Both the 256GB and 512GB models are equipped with that much cache whereas the 128GB Samsung 840 Pro comes with 256 MB of cache. And third, we can see eight flash memory chips with Toggle Mode 2.0 interface. Each of them has a capacity of 32 GB and contains four 64-gigabit MLC NAND devices manufactured on Samsung’s 21nm facilities. Thus, the MDX controller can use 4-way interleaving on each of its eight channels in the 256GB SSD.
Here is a summary of the Samsung 840 Pro 256GB specifications:
The new controller's high performance helped implement AES-256 encryption in the Samsung 840 Pro. You can enable it and enter the encryption key through the mainboard’s BIOS.
Excellent software support is yet another advantage of Samsung's SSDs. The Samsung Magician utility is one of the best tools for working with SSDs. It is as good as Intel SSD Toolbox in its functionality.
Besides standard functions (viewing SMART information, updating firmware and performing Secure Erase), the Magician utility provides a number of extras including a synthetic performance benchmark.
It can optimize OS settings for SSDs and issue the TRIM command.
It can also create a reserve pool on the SSD (up to 10% of its total capacity) that is used for more efficient garbage collection and helps improve the device's service life in high-load environments.
It must be noted that even without any tricks with Magician the formatted capacity of a Samsung 840 Pro 256GB is 238 gibibytes, so the manufacturer has already allotted 7% of the drive's total capacity for the reserve pool. Considering that the Samsung 840 Pro is positioned as a professional solution, it is no wonder that it comes with a 5-year warranty.
As manufacturing technologies get better, synchronous MLC NAND flash memory has made inroads in relatively inexpensive SSDs. We mean popular flash memory types whereas the Samsung 840 Pro uses rather rare 21nm MLC NAND flash with Toggle Mode 2.0 interface, which is not inexpensive at all. The Pro version of Samsung's new SSD may only be marketed in the same price category with flagship SSDs from other brands. It is not a mass-market product. That's why Samsung has also prepared an affordable modification as well. The basic Samsung 840 features the same hardware platform but MLC NAND is replaced in it with cheaper TLC NAND (Triple Level Cell) flash which stores not two but three bits of data in each memory cell.
TLC NAND is not an innovation. It is used widely in USB flash drives. However, it is the first time we see it in an SSD, so the Samsung 840 is kind of experimental. TLC NAND is cheaper than the popular MLC NAND and also inferior to it across many parameters. Particularly, it has lower access speed and, which is even worse, shorter service life. The following table illustrates this fact:
TLC NAND flash can store not two but three bits of data in each memory cell by increasing the number of electrical charge levels on the transistor’s floating gate from four to eight. However, it becomes harder to recognize the signal and programming such memory cells requires higher voltage which leads to faster deterioration in the semiconductor design. The higher bit density results in smaller physical size. MLC NAND needs 1.5 times more transistors to store the same amount of data as TLC NAND flash. And since the transistors are actually the same, TLC NAND flash is supposed to be 1.5 times cheaper than MLC NAND flash.
Using TLC memory in inexpensive SSDs is an attractive opportunity but no one has ever tried to do that as yet. The manufacturers and users have apprehensions about its low service life which is declared to be 1000 program/erase cycles. However, a simple computation can show that, assuming a realistic write amplification coefficient of 3x, saving 20 GB of data to a TLC-based 256GB SSD daily will only make it fail in 11 years. A 128GB SSD will last only half that time, but it is still more than enough for a consumer-class SSD.
So, the Samsung 840 is a compromise. It is theoretically not as long-lasting as SSDs with MLC NAND flash but, on the other hand, it represents an inexpensive version of one of the fastest SSD platforms available. Samsung is quite confident about its reliability, shipping this inexpensive SSD with a standard 3-year warranty.
The Samsung 840 doesn’t differ much from its Pro cousin in accessories or appearance. The manufacturer obviously doesn’t want to emphasize its entry-level positioning or inferiority, so it looks as noble as the Samsung 840 Pro. Its box is just slightly different in design, using gray as the predominant color. The picture on the front of the packaging shows the SSD en face rather than in an isometric view.
Like the Pro version, the basic 840 comes with some documentation and a CD with electronic manual and software. There is no adapter to mount it into 3.5-inch system case bays. There are also no frames or something to increase its thickness from 7 to 9.5 mm.
The SSD looks identical to its senior cousin, so you can only differentiate the 840 Pro and the basic 840 by the info sticker on the bottom surface of the unified case.
Considering that the Samsung 840 uses the same hardware platform as the flagship model, there's a familiar PCB inside but some of the chips populating it are different.
The memory chips are labeled K9CFGY8U5A-CCK0 rather than K9HFGY8U5A-CCK0, so it is TLC NAND, even though the chip design is the same. Each chip contains four 21nm semiconductor dies with Toggle Mode 2.0 interface. There are eight chips in total, each with a capacity of 32 GB and the Samsung 840 uses 4-way interleaving on each controller channel.
Otherwise, the Samsung 840 has the same components as its senior cousin including a 512MB LPDDR2-1066 SDRAM chip for cache (it is labeled K4P4G324EB-FGC2). The controller is the same, too. Thus, the Samsung 840 retains the key advantage of the Pro version, its high-performance triple-core processor. The lower specified read and write speeds are only due to the higher-latency flash memory.
Here is a summary of the Samsung 840 250GB specifications:
Judging by the official specs, the slower TLC memory affects write speed in the first place, the Samsung 840 being only half as fast as the Samsung 840 Pro at writing. The read speeds don’t differ that much. One more thing to be noted is that the Samsung 840’s storage capacity is 6 GB smaller because the reserve pool is larger at 9% of the total capacity. This may help to make up for the shorter service life of TLC memory.
Although the Samsung 840 is an inexpensive product, its manufacturer didn’t deliberately strip it of extra features. Like the Pro model, it supports AES encryption with a 256-bit key and is compatible with the exclusive Magician utility.
In other words, the Samsung 840 offers the same functionality as the Pro model. The difference is in performance and, theoretically, in service life, which is reflected in the shorter warranty period.
For our today’s SSD test session we use a unified test system built on an Intel H77 based mainboard, which features two SATA 6 Gbit/s ports. We will use these ports to connect the tested SSDs.
As for the today’s testing participants, it is obvious that Samsung 840 Pro 256 GB and Samsung 840 250 GB SSDs must be compared against the most current offering from other vendors. Therefore, you will see on the diagrams the performance numbers for versatile popular products based on SandForce, Marvell, LAMD and Indilinx controllers, as well as the representatives of Samsung’s previous SSD generation. The LSI SF-2281 is represented by the today’s fastest product based on it - Intel SSD 520, as well as a typical solid state drive - Corsair Force GS. LAMD LM87800 controller will be tested in Corsair Neutron GTX and Corsair Neutron SSDs. OCZ Vertex 4 and OCZ Vector defended the honor of the Indilinx Everest 2 and Indilinx Barefoot 3 controllers. Marvel platform was brought in by Plextor M5S on Marvell 9174 controller, and Plextor M5 Pro based on a more up-to-date Marvell 9187 controller. And of course, we couldn’t leave out the previous generation Samsung 830 SSD on the MCX controller. All above mentioned SSDs use exclusively synchronous MLC flash memory. Corsair Neutron, Intel SSD 520, OCZ Vertex 4, OCZ Vector and Plextor M5S are built with 25 nm memory from IMFT consortium with ONFI-interface. Corsair Force GS, Corsair Neutron GTX and Plextor M5 Pro use Toggle Mode MLC NAND manufactured by Toshiba using 2x nm or 19 nm production process. As for Samsung SSDs, I would like to remind you that they use their own memory: it used to be 27 nm Toggle Mode MLC NAND, but now the new drives are designed with 21 nm MLC and TLC NAND with Toggle Mode 2.0 interface. We did our best to ensure that all testing participants came in the closest storage capacity, to ensure fairness of the comparison.
Overall our testbed was configured as follows:
We use Anvil's Storage Utilities 1.0.51 to measure random and sequential ref and write speeds. The synthetic benchmark integrated into this software suite provides a great overview of the products by experimentally checking out a wide variety of speed characteristics of the tested SSD.
The results you see here refer to the FOB (fresh out-of-box) non-degraded SSD performance. Moreover, we use incompressible data, which is formally the least favorable scenario for the LSI SF-2281 controller that employs on-the-fly data compression. Our tests show, however, that in today’s world when the data may only be partially compressed and the utilized flash memory has high-speed synchronous interface, the compression algorithms do not have a big effect on the real-life performance of SSDs with SandForce controllers. Therefore, we gave up the idea of testing SandForce-based SSDs with compressible data: These results would be exclusively artificial in nature and wouldn’t have any practical value for us today.
As promised by Samsung, the new 840 Pro claims to be the fastest desktop SSD available today. We can see that in our synthetic benchmarks. Its read speed is unrivalled at most popular types of operations, being only inferior to the read speed of the Plextor M5 Pro when the request queue is very long. The Samsung 840 Pro is good at writing as well, but its result is rather average when it comes to random-address writing with a small request queue.
The basic Samsung 840 is slower than its senior cousin. It is good at sequential reading and at reading large data blocks, but the high latency of its TLC NAND flash lets it down at writing and at processing 4KB data blocks. That said, the Samsung 840 does offer rather good performance for its low price. It is no worse than its predecessor Samsung 830 and can compete with such popular products as OCZ Vertex 4, Plextor M5S and Corsair Neutron. Samsung engineers seem to have made up for the high latency of TLC NAND flash in some way or another, so this SSD doesn’t look like an outsider among products with MLC NAND flash.
Unfortunately, SSDs are not always as fast as in their “fresh” state. In most cases their performance goes down after some time and in real life we deal with completely different write speeds than what we see on the diagrams in the previous chapter of our review. The reason for this phenomenon is the following: as the SSD runs out of free pages in the flash memory, its controller has to clear memory page blocks before saving data into them, which causes substantial delays. Therefore, contemporary SSDs usually try to free the memory in advance, and not when writes are underway. This usually happens in idle mode. At this time SSD controller can alleviate the performance drop almost completely by erasing unused flash memory pages ahead of time. The corresponding procedures are usually performed in idle mode, when the controller can fully restore the SSD performance by clearing out the unused flash memory pages. They use two techniques for that: idle-time garbage collection and TRIM.
An SSD controller doesn’t know which memory pages contain user data and which are considered empty by the OS. It happens this way because in file systems removing a file doesn’t involve its actual physical removal. Instead, the corresponding memory is marked in the file system as available for rewriting into. So, without involving the OS, an SSD controller can only pre-erase pages in the reserve pool (if it exists), which is not accessible by the OS. For a better solution to this problem, modern OSes have the TRIM command which improves garbage collection the efficiency. TRIM provides the SSD controller with information on which data could potentially be removed without any harm, as it is considered unused by the OS. As a result, the SSD controller can increase the cleared pages pool by physically removing unneeded data so that the user didn’t feel a performance hit during subsequent write requests.
This is how it should be in an ideal world. In reality, however, SSDs differ in their garbage collection and TRIM implementation. That’s why we check out the performance hit an SSD suffers when transitioning from its out-of-box (the flash memory is clean) to steady-state. This test follows the SNIA SSSI TWG PTS guidelines, which means that we measure the write speed in four cases one by one. First we measure the “fresh” SSD speed. Then we measure the speed after the SSD has been fully filled with data twice. The third test occurs after a 30-minute break during which the controller can partially restore performance by running the idle-time garbage collection. And finally, we measure the speed after issuing a TRIM command.
We ran the tests in synthetic IOMeter 1.1.0 RC1 benchmark, where we measured random write speed when working with 4 KB data blocks aligned to flash memory pages at 32 requests queue depth. The test data were pseudo-random. The following diagram shows the history of the relative speed changes, where 100% refers to the SSD performance in “fresh-out-of-box” state.
The diagram suggests that the performance degradation problem only plagues SandForce-based products. The rest of the SSDs can restore their performance after receiving the TRIM command from the OS. That’s true for Samsung's 840 Pro and 840, too. Their speed is restored just as expected. Thus, these SSDs are not susceptible to performance degradation in the majority of modern OSes.
On the other hand, garbage collection doesn’t work on the new Samsung drives without TRIM, which should be taken into account by users of non-TRIM environments. Samsung’s Magician utility can be used to send the TRIM command to the drive manually, but it only exists in Windows-compatible versions. So if you have some problems with TRIM support, you may want to choose other products such as the Plextor or Corsair drives with LAMD controllers.
The popular PCMark 7 contains an individual disk subsystem benchmark. It is not a synthetic test, but is based on real-life applications. This benchmark reproduces typical disk usage scenarios and measures how fast they are completed in popular tasks. Starting with version 1.4.0, the PCMark 7 disk subsystem test generates raw performance results which do not take into account any pauses in the requests queue. New results are thus incompatible with old ones, but the differences between the performance numbers of different SSDs have now become more obvious. That’s why we decided to switch to the new version of the test from now on.
We ran PCMark 7 on “steady” SSDs, which is what they are going to be in actual computer systems most of the time. Their performance in this case is affected not only by their controller or flash memory speed but also by the efficiency of their internal algorithms that fight performance degradation.
The Samsung 840 Pro is the first SSD to beat SandForce-based products in PCMark 7, this benchmark being very favorable to the SandForce controller. It is an important victory that proves how powerful Samsung’s new SSD platform is. The Samsung 840 with TLC flash is, on the contrary, at the bottom of the diagram, even losing to its 830 series predecessor.
Let’s figure out what happened. The total PCMark 7 score is a more generalized performance metric. We will check out the individual tests to get a more detailed picture of what our SSDs are capable of under various types of operational load:
The Samsung 840 Pro proves its premium class again. It takes the lead in the most important usage scenarios and only falls behind its opponents when it comes to processing small multimedia files. The basic Samsung 840 behaves in the same way but has lower speed due to its TLC NAND flash. Thus, the poor overall score of this SSD is determined by its low performance with audio and image files. When it comes to the system scenarios or to processing large files, the Samsung 840 is quite an average product in performance, comparable even to the OCZ Vector or the Corsair Neutron GTX.
Intel NASPT is another disk sub-system test that employs real-life usage scenarios. Like PCMark 7, Intel NASPT reproduces predefined disk activity traces and measures how fast they are executed. However, the default traces are designed for network attached storage devices rather than for SSDs. Therefore during our test session we replace them with the specially developed SSD Benchmarking Suite which offers more relevant usage scenarios such as compressing and decompressing files, compiling large projects, copying files and folders, loading 3D game levels, installing software, batch-processing photos, searching a digital library for data, mass-launching applications, and transcoding video.
Like PCMark 7, this benchmark gives us a true-to-life illustration of disk subsystem performance. Here the SSDs are again tested in their “steady” state.
Intel’s NASPT seems to show a more realistic picture of performance, and the Samsung 840 Pro is on top again, enjoying a large advantage over its opponents. There is no doubt that it is the fastest SSD available today. The ex-leaders OCZ Vector and Plextor M5 Pro look quite mediocre in comparison.
The inexpensive Samsung 840 isn’t bad, either. Using slower TLC flash, it is quite fast by today’s standards. For example, it is ahead of any SandForce-based SSD and beats the popular OCZ Vertex 4 and Corsair Neutron.
Besides the average benchmark score, we would also like to offer you the results of individual usage scenarios, which will show where new Samsung SSDs can really shine. Note that the data-transfer rate is higher than the SATA 3 interface bandwidth in some subtests. That’s because INASPT is a high-level test that uses standard Windows functions to access the disk subsystem. As a result, the OS caching mechanisms also affect the results.
Samsung’s platform is especially good at processing large files, but delivers high performance in every other case, too. According to Intel’s NASPT, the Samsung 840 Pro isn’t a perfect system disk. The Intel 520 may be a better choice for certain usage scenarios thanks to its customized firmware. However, even Intel NASPT suggests that the Samsung 840 Pro is the best versatile SSD for a broad range of applications.
The Samsung 840 looks good, too. Its performance/price ratio is very attractive. Its speed isn’t very high when you have to write a lot of data on it, but such tasks aren’t very typical for SSDs. Otherwise, this inexpensive Samsung 840 is comparable to the Plextor M5S or Corsair Neutron.
We use AS SSD version 1.7.4739.38088 test to benchmark the speed of copying different types of files within a single partition the size of the whole SSD. The SSDs are tested in their steady state.
Copying means reading and writing concurrently, and the Samsung 840 with its slow TLC NAND flash is comparable to the SandForce-based drives with synchronous MLC flash. The flagship Samsung 840 Pro model, even though fast enough, cannot win this test. It is inferior to the Corsair Neutron GTX or OCZ Vector depending on the type of files.
With the introduction of new SSDs Samsung puts forth a strong claim to the leading position on the consumer-class SSD market. Besides manufacturing all of SSD components and thus having more elbowroom for price maneuvering, the company has got a very high-performance platform which combines a triple-core MDX controller and 21nm Toggle Mode 2.0 flash.
Of course, it is the senior model, Samsung 840 Pro, which provokes the sensation. Based on MLC memory, it is definitely better than previous leaders in terms of speed. Thanks to its high-speed controller, it offers an impressive random read speed even at a short request queue, so it is superior to other SSDs under real-life desktop or notebook loads. Our testing shows that the Samsung 840 Pro is the fastest SATA 3 SSD available now. Added to this are its 5-year warranty, integrated AES-256 encryption and excellent software support. Of course, the Samsung 840 Pro is not cheap, but it is no more expensive than other flagship SSDs.
The inexpensive Samsung 840 doesn’t look that effective in diagrams in comparison with its senior cousin. It is limited by its cheap high-latency TLC flash but its MDX controller makes up for that to some extent. As a result, the Samsung 840 is quite competitive in everyday applications against popular midrange SSDs with MLC NAND flash, such as the OCZ Vertex 4, Plextor M5S and Corsair Neutron. Thus, the Samsung 840 features a most attractive price/performance ratio. Its TLC memory has a service life of 1000 program/erase cycles, which makes it less long-lasting than other SSDs. Even though its warranty period is 3 years and there are no reports of it failing too soon, some users may shun it for that reason. That’s why we wouldn’t make any recommendations about it. We can only note that it is quite an interesting SSD with peculiarities of its own.
To help you with your choice, we offer the following summary table with test results of various SSDs. It contains basic hardware information about SSDs we’ve tested so far and allows to quickly determine the general position of a particular model among its competitors in terms of relative performance.