The Introduction, The Drive & The test Performance Consistency & TRIM Validation Storage Bench 2013 Storage Bench 2011 Random & Sequential Performance Performance vs. Transfer kích cỡ Power Consumption Final Words

Two years ago Samsung dropped the bomb by releasing the first TLC NAND based SSD. I still vividly remember Anand's reaction when I told him about the SSD 840. I was in Korea for the launch event and was sitting in a press room where Samsung held the announcement. Samsung had only sampled us & everyone else with the 840 Pro, so the 840 & its guts had remained as a mystery. As soon as Samsung lifted the curtain on the 840 specs, I shot Anand a message telling him that it was TLC NAND based. The reason why I still remember this so clearly is because I had to lớn tell Anand three times that, "Yes, I am absolutely sure và am not kidding" before he took my word.

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For nearly two years Samsung was the only manufacturer with an SSD that utilized TLC NAND. Most of the other manufacturers have talked about TLC SSDs in one way or another, but nobody has come up with anything retail worthy... Until now. A month ago SanDisk took the stage & unveiled their Ultra II, the company's first TLC SSD và the first TLC SSD that is not by Samsung. Obviously, there's a lot to lớn discuss, but let's start with a quick overview of TLC và the market landscape.


There are a variety of reasons for Samsung's head start in the TLC game. Samsung is the only client SSD manufacturer with a fully integrated business model: everything inside Samsung SSDs is designed & manufactured by Samsung. That is chất lượng in the industry because even though the likes of SanDisk and Micron/Crucial manufacture NAND and develop their own custom firmware, they rely on Marvell's controllers for their client drives. Third tiệc ngọt silicon always creates some limitations because it is designed based on the needs of several customers, whereas in-house silicon can be designed for a specific application và firmware architecture.

Furthermore, Samsung is the only NAND manufacturer in addition khổng lồ SK Hynix that is not in a NAND joint-venture. Without a partner Samsung has the full freedom to dedicate as much (or as little) resources & fab space to TLC development & production as necessary, while SanDisk must coordinate with Toshiba to lớn ensure that both companies are satisfied with the development và production strategy.

From what I have heard, the two major problems with TLC have been late production ramp up and low volume. In other words, it has taken two or three additional quarters for TLC NAND to lớn become mature enough for SSDs compared lớn MLC NAND at the same node, which means that a new MLC node is already sampling and will be available for SSD use within a couple of quarters. It has simply made sense khổng lồ wait for the smaller và more cost efficent MLC node to lớn become available instead of focusing development resources on a TLC SSD that would become obsolete in a matter of months.

SanDisk & Toshiba seem to lớn have revised their strategy, though, because their second generation 19nm TLC is already SSD-grade & the production of both MLC & TLC flavors of the 15nm node are ramping up as we speak. Maybe TLC is finally becoming a first class citizen in the fab world. Today's reviews will help tell us more about the state of TLC NAND outside of Samsung's world. I am not going to cover the technical aspects of TLC here because we have done that several times before, so take a look at the links in case you need a refresh on how TLC works và how it differs from SLC/MLC.


The Ultra II is available in four capacities: 120GB, 240GB, 480GB and 960GB. The 120GB & 240GB models are shipping already, but the larger 480GB and 960GB models will be available in about a month. All come in a 2.5" 7mm khung factor with a 9.5mm spacer included. There are no mSATA or M.2 models available và from what I was told there are not any in the pipeline either (at least for retail). SanDisk has always been rather conservative with their retail lineup & they have not been interested in the small niches that mSATA and M.2 currently offer, so it is logical decision khổng lồ stick with 2.5" for now.

SanDisk Ultra II Specifications
ControllerMarvell 88SS9190Marvell 88SS9189
NANDSanDisk 2nd ren 128Gbit 19nm TLC
Sequential Read550MB/s550MB/s550MB/s550MB/s
Sequential Write500MB/s500MB/s500MB/s500MB/s
4KB Random Write80K IOPS83K IOPS83K IOPS83K IOPS
Idle nguồn (Slumber)75mW75mW85mW85mW
Max power (Read/Write)2.5W / 3.3W2.7W / 4.5W2.7W / 4.5W2.9W / 4.6W
WarrantyThree years
Retail Pricing$80$112$200$500

There are two different controller configurations: the 120GB and 240GB models are using the 4-channel 9190 "Renoir Lite" controller, whereas the higher capacity models use the full 8-channel thiết kế 9189 "Renoir" silicon. To lớn my knowledge there is not any difference besides the channel count (perhaps in internal cache sizes too), và the "Lite" version is cheaper. SanDisk has done this before with the X300s for instance, so having two different controllers is not really anything new và it makes sense because the smaller capacities cannot take full advantage of all eight channels anyway. Lưu ý that the 9189/9190 is not the new TLC-optimized 1074 controller from Marvell – it is the same controller that is used in Crucial's MX100 for example.

Similar lớn the rest of SanDisk's client SSD lineup, the Ultra II does not offer any encryption support. For now SanDisk is only offering encryption in the X300s, but in the future TCG Opal 2.0 và eDrive support will very likely make their way to lớn the client drives as well. DevSleep is not supported either và SanDisk said the reason is that the niche for aftermarket DevSleep-enabled SSDs is practically non-existent. Nearly all platforms that tư vấn DevSleep (which is very few, actually) already come with SSDs, e.g. Laptops, so DevSleep is not a feature that buyers find valuable.

nCache 2.0

The Ultra II offers rather impressive performance numbers for a TLC drive as even the smallest 120GB model is capable of 550MB/s read and 500MB/s write. The secret behind the performance is the new nCache 2.0, which takes SanDisk's pseudo-SLC caching mode to lớn a next level. While the original nCache was mainly designed for caching the NAND mapping table along with some small writes (nCache 2.0 OverviewCapacity120GB240GB480GB960GBSLC Cache Size5GB10GB20GB40GB

The interesting tidbit about SanDisk's implementation is the fact that each NAND die has a fixed number of blocks that run in SLC mode. The benefit is that when data has to lớn be moved from the SLC to lớn the TLC portion, the transfer can be done internally in the die, which is a feature SanDisk calls On cpu Copy. This is a proprietary design và uses a special die, so you will not see any competitive products using the same architecture. Normally the SLC lớn TLC transfer would be done lượt thích any other wear-leveling operation by using the NAND interface (Toggle or ONFI) và DRAM to move the data around internally from die to die, but the downside is that such a kiến thiết may interrupt host IO processing since the internal operations occupy the NAND interface & DRAM.

OCZ's "Performance Mode" is a good example of a competing technology: once the fast buffer is full the write speed drops lớn half because in addition to lớn the host IOs, the drive now has khổng lồ move the data from SLC lớn MLC/TLC, which increases overheard since there is additional load on the controller, NAND interfaces, & in the NAND itself. Performance recovers once the copy/reorganize operations are complete.

SanDisk's approach introduces minimal overhead because everything is done within the die. Since an SLC block is exactly one third of a TLC block, three SLC blocks are simply folded into one TLC block. Obviously there is still some additional latency if you are trying lớn access a page in a block that is in the middle of the folding operation, but the impact of that is far smaller than what a die-to-die transfer would cause.

The On chip Copy has a predefined threshold that will trigger the folding mechanism, although SanDisk said that it is adaptive in the sense that it will also look at the data type and kích thước to determine the best action. Idle time will also trigger On chip Copy, but there is no set threshold for that either from what I was told.


In our 240GB sample the SLC cache size is 10GB và since sixteen 128Gbit (16GiB) NAND dies are needed for the raw NAND capacity of 256GiB, the cache per die works out lớn be 625MB. I am guessing that in reality there is 32GiB of TLC NAND running in SLC mode (i.e. 2GiB per die), which would mean 10.67GiB of SLC, but unfortunately SanDisk could not cốt truyện the exact block sizes of TLC & MLC with us for competitive reasons.

The performance benefits of the SLC mode are obvious. A TLC block requires multiple iterations to lớn be programmed because the distribution of the voltage states is much narrower, so there is less room for errors, which needs a longer and more complex programming process.


I ran HD Tach to lớn see what the performance is across all LBAs. With sequential data the threshold for On chip Copy seems to be about 8GB because after that the performance drops from 400MB to ~230MB/s. For average client workloads that is more than enough because users vì not usually write more than ~10GB per day and with idle time nCache 2.0 will also move data from SLC to lớn TLC khổng lồ ensure that the SLC cache has enough space for all incoming writes.

The improved performance is not the only benefit of nCache 2.0. Because everything gets written lớn the SLC portion first, the data can then be written sequentially khổng lồ TLC. That minimizes write amplification on the TLC part, which in turn increases endurance because there will be less redundant NAND writes. With sequential writes it is typically possible to achieve write amplification of very close to lớn 1x (i.e. The minimum without compression) & in fact SanDisk claims write amplification of about 0.8x for typical client workloads (for the TLC portion, that is). That is because not all data makes it lớn the TLC in the first place – some data will be deleted while it is still in the SLC cache and thus will not cause any wear on the TLC. Remember, TLC is generally only good for about 500-1,000 P/E cycles, whereas SLC can easily surpass 30,000 cycles even at 19nm, so utilizing the SLC cache as much as possible is crucial for endurance with TLC at such small lithographies.

Like the previous nCache 1.0, the 2.0 version is also used to lớn cache the NAND mapping table lớn prevent data corruption & loss. SanDisk does not employ any nguồn loss protection circuitry (i.e. Capacitors) in client drives, but instead the SLC cache is used khổng lồ flush the mapping table from the DRAM more often, which is possible due to lớn the higher endurance & lower latency of SLC. That obviously does not provide the same cấp độ of protection as capacitors do because all writes in progress will be lost during a power nguồn failure, but it ensures that the NAND mapping table will not become corrupt và turn the drive into a brick. SanDisk actually has an extensive whitepaper on nguồn loss protection and the techniques that are used, so those who are interested in the topic should find it a good read.

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Multi Page Recovery (M.P.R)

Using parity as a size of error correction has become more and more popular in the industry lately. SandForce made the first move with RAISE several years ago & nearly every manufacturer has released their own implementation since then. However, SanDisk has been one of the few that have not had any proper parity-based error correction in client SSDs, but the Ultra II changes that.

SanDisk's implementation is called Multi Page Recovery & as the name suggests, it provides page-level redundancy. The idea is exactly the same as with SandForce's RAISE, Micron's RAIN, and any other RAID 5-like scheme: parity is created for data that comes in, which can then be used to recover the data in case the ECC engine is not able to do it.

The parity ratio in the Ultra II is 5:1, which means that there is one parity page for every five pages of actual data. But here is the tricky part: with 256GiB of raw NAND and a 5:1 parity ratio, the usable capacity could not be more than 229GB because one sixth of the NAND is dedicated for parity.

The secret is that the NAND dies are not really 128Gbit – they are in fact much larger than that. SanDisk could not give us the exact form size due to lớn competitive reasons, but told us that the 128Gbit number should be treated as MLC for it khổng lồ make sense. Since TLC stores three bits per cell instead of two, it can store một nửa more data in the same area, so 128Gbit of MLC would become 192Gbit of TLC. That is in a perfect world where every die is equal and there are no bad blocks; in reality TLC provides about a 30-40% mật độ trùng lặp từ khóa increase over MLC because TLC inherently has more bad blocks (e.g. Stricter voltage requirements because there is less room for errors due to lớn narrower distribution of the voltage states).

In this example, let's assume that TLC provides a 35% increase over TLC when the bad blocks are taken away. That turns our 128Gbit MLC die into a 173Gbit TLC die. Now, with nCache 2.0, every die has about 5Gbit of SLC, which eats away ~15Gbit of TLC và we over up with a die that has 158Gbit of usable capacity. Factor in the 5:1 parity ratio & the final user capacity is ~132Gbit per die. Sixteen of those would equal 264GiB of raw NAND, which is pretty close to the 256GiB we started with.

Note that the above is just an example to lớn help you understand how 5:1 parity ratio is possible. Like I said, SanDisk would not disclose the actual numbers và in the real world the raw NAND capacity may vary a bit because the number of bad blocks will vary from die khổng lồ die. What matters, though, is that the Ultra II has the same 12.7% over-provisioning as the Extreme Pro, and that is after nCache 2.0 and Multi Page Recovery have been taken into trương mục (i.e. 12.7% is dedicated to lớn garbage collection, wear-leveling và the usual NAND management schemes).

Furthermore, all NAND die have what are called spare bytes, which are additional bytes meant for ECC. For instance Micron's 20nm MLC NAND has an actual page kích thước of 17,600 bytes (16,384 user space + 1,216 spare bytes), so in reality a 128Gbit die is never truly 128Gbit – there is always a bit more for ECC & bad block management. The number of spare bytes has grown as the industry has moved khổng lồ smaller process nodes because the need for ECC has increases và so has the number of bad blocks. TLC is just one cấp độ worse because it is less reliable by its design, hence more spare bytes are needed lớn make it usable in SSDs.

Testing Endurance

SanDisk does not provide any specific endurance rating for the Ultra II, which is similar to what Samsung is doing with the SSD 840 EVO. The reason is that both are only validated for client usage, meaning that if you were khổng lồ employ either of them in an enterprise environment, the warranty would be void anyway. I can see the reasoning behind not including a strict endurance rating for an entry-level client drive because consumers are not very good at understanding their endurance needs and having a rating (which would obviously be lower for a TLC drive) would just lead to lớn confusion. However, the fact that SanDisk has not phối any rating does not mean that I am not going to test endurance.


To vày it, I turned lớn our standard endurance testing methodology. Basically, I wrote sequential 128KB data (QD1) to lớn the drive & monitored the SMART values 230 & 241, i.e. Truyền thông media Wear Out Indicator (MWI) và Total GB Written. In the case of the Ultra II, the MWI works opposite of what we are used to: it starts from 0% & increases as the drive wears out. When the MWI reaches 100%, the drive has come to lớn the end of its rated lifespan – it will likely continue khổng lồ work because client SSD endurance ratings are with one-year data retention, but I would not recommend using it for any crititical data after that point.

SanDisk Ultra II Endurance Test
Change in media Wear Out Indicator7.8%
Change in Total GB Written9,232GiB
Observed Total Endurance118,359GiB
Observed P/E Cycles~530

The table above summarizes the results of my test. The duration of the test was 12 hours and I took a few data points during the run lớn ensure that the results are valid. From the data, I extrapolated the total endurance and used it as the basis khổng lồ calculate the P/E cycles with the following formula:


I made the assumption that the combined Wear Leveling and Write Amplification factor is 1x because that is plausible with pure sequential writes & it makes the calculation much simpler. For capacity I used the user capacity (240GB i.e. 223.5GiB), so the observed P/E cycles is simply total endurance divided by the capacity (both in GiB).

The number I came up with is 530 P/E cycles. There are a number of factors factors that make it practically impossible to lớn figure out the exact NAND endurance because a part of the NAND operates in SLC mode with far greater endurance and there is a hefty amount of spare bytes for parity, but I think it is safe to lớn say that the TLC NAND portion is rated at around 500 P/E cycles.

SanDisk Ultra II Estimated Endurance
Total Estimated Endurance54.6TiB109.1TiB218.3TiB436.6TiB
Writes per Day20GiB
Write Amplification1.2x
Total Estimated Lifespan6.4 years12.8 years25.5 years51.0 years

Because the P/E cycle count alone is easy to misunderstand, I put it into context that is easier to lớn understand i.e. Lifespan of the drive. All I did was multiply the user capacity by the P/E cycle count lớn get the total endurance, which I then used to calculate the estimated lifespan. I selected 20GiB of writes per day because even though SanDisk did not provide an endurance rating for the Ultra II, their internal kiến thiết goal was 20GiB per day, which is a fairly common standard for client drives. I phối the write amplification to lớn 1.2x as the TLC blocks are written sequentially thanks lớn nCache 2.0, và that should result in write amplification that is very close to lớn 1x.

500 P/E cycles certainly does not sound much, but when you put it into context it is more than enough. At 20GiB a day, even the 120GB Ultra II will easily outlive the rest of the components. NCache 2.0 plays a huge role in making the Ultra II as durable as it is because it keeps the write amplification close to lớn the ideal 1x. Without nCache 2.0, 500 P/E cycles would be a major problem, but as it stands I vì chưng not see endurance being an issue. Of course, if you write more than 20GiB per day and your workload is IO intensive in general, it is better khổng lồ look for drives that are meant for heavier usage, such as the Extreme Pro và SSD 850 Pro.

A look at SanDisk's Updated SSD Dashboard

Along with the Ultra II, SanDisk is bringing an updated version of its SSD Dashboard, labeled as 1.1.1.


The start view has not changed & provides the same overview of the drive as before.


The most important new features are under the "Tools" tab and are provided by third parties. In the past SanDisk has not offered any cloning software with their drives, but the new version brings the option lớn use Apricorn's EZ GIG IV software lớn migrate from an old drive. Clicking the links in the Dashboard will lead to lớn Apricorn's website where the user can tải về the software. Cảnh báo that the Dashboard includes a special version of EZ GIG IV that can only be used lớn clone a drive once.

In addition khổng lồ EZ GIG IV, the 1.1.1 version adds Trend Micro's Titanium Antivirus+ software. While most people are already running antivirus software of some sort, there are (too) many people who vì chưng not necessarily have an up-to-date antivirus software that has the definitions for the latest malware, so the idea behind including the antivirus software is lớn ensure that all users have a free and easy way to check their system for malware before migrating to a new drive.

The new version also adds tư vấn for "sanitation". It is basically an enhanced version of secure erase và works the same way as 0-fill erase does: instead of just erasing the data, sanitation writes zeros khổng lồ all LBAs khổng lồ guarantee that there is absolutely no way lớn recover the old data. Crypto erase is now a part of the Dashboard too, although currently that is only supported by the X300s since it is the only drive with hardware encryption support.


Live performance monitoring is also supported, but unfortunately there is no option to run a benchmark within the software (i.e. It just monitors the drive similar to lớn what Windows Performance Monitor does). For OSes without TRIM, the Dashboard includes an option to run a scheduled TRIM lớn ensure maximum performance. If TRIM is tư vấn and enabled (like in this case since I was running Windows 8.1), the TRIM tab is grayed out since the OS will take care of sending the TRIM commands when necessary.


Support has also been improved in the new version as options for live chat & email support have been added. New languages have been added, too, and the Dashboard is now available in 17 different languages. During the install process, the installer will ask for the preferred language, but it is also possible khổng lồ change that afterwards under the Settings tab.

Test Systems

For Storage Benches, performance consistency, random and sequential performance, performance vs transfer size and load power nguồn consumption we use the following system:

Thanks toG.Skillfor theRipjawsX 32GB DDR3 DRAM kit

For slumber power testing we used a different system: