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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SSDFDE - Wednesday, November 14, 2012 - link
... actually what happens if I set the IDE (sorry, its ATA actually) password in BIOS and then move the drive to another computer with no ATA HDD BIOS password set? Will it be readable there as the internal key in the drive of course still is the same?As ATA password is an option only, and setting the ATA password does not alter the internal SSD key, the actual encryption on the drive does not change at all no matter if a ATA password is set or not, right?
BTW: Resetting / generating an new internal key seems to be done with "secure erase" on hardware-encrypted drives with internal encryption key... clearly then its only bitshit on the dive once the old key is lost. Is there an option to do that an the Samsung drive anyway?
JellyRoll - Saturday, November 24, 2012 - link
Digital Signal Processing has nothing to do with the voltage states of the NAND. It is processing of the actual signal that comes from the NAND packages.DSP is used for multiple technologies, from audio to video to radar. These devices do not utilize nand, and DSP has zero interaction with the NAND itself, it merely reduces and corrects the amount of errors that come from the NAND.
here is a primer on DSP: http://www.analog.com/en/content/beginners_guide_t...
There needs to be more research before these incorrect explanations are posted.
"Even though DSP doesn't make NAND immortal, it causes a lot less stress on the NAND, allowing it to last for more P/E cycles than what you would get without DSP."--This statement is entirely untrue, as DSP has no interaction with the NAND itself. It seems there is a bit of guesswork going on when writing this article.
DSP simply corrects errors. With lower endurance NAND you experience more errors.
PanzerIV88 - Thursday, December 27, 2012 - link
I just bought on Boxing Day that Samsung 840 250Gb for 150$ + Taxes. The sequential write speed is what scares the most but other than marketing bs it's actualy what's the less important. There's much more happening into the small files or reading speed which it shines in. I'll definitely replace my Vertex 4 128Gb which isn't as amazing as I thought it was, mostly since I learned that once it reaches 50% capacity, it turns into storage mode instead of performance and the write speed falls of 2 to 3x!!! I can confirm this with benchs I've done, it's really sad..Also thought of doing a Vertex 4 Raid 0 but other than bragging with bench numbers, seriously wtf does 600-800Mb/s is gonna do for a daily light load or gaming?! Totaly nothing more... so I'll save my money.
sriggins - Saturday, March 16, 2013 - link
I have been using an 830 in my MacBook Pro since last October. I use FileVault 2 and do a ton of compiling on the drive. Performance has been steady. How does using OS X encryption affect the life of the drive? Is there any way to tell how many writes have been done so far?brainfuck - Wednesday, July 3, 2013 - link
Is there any way to find the Erase Block Size of Samsung 840 250GB?so that i can align my disk accordingly
thanks
WildBillvms - Wednesday, May 21, 2014 - link
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