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
Lower Endurance: Hardly an Issue
With perfect wear-leveling and write amplification of 1x, you would get 256,000GiB (that's ~275TB) of writes out of a 250GB Samsung 840 with TLC NAND and 1,000 P/E cycles. That is still a lot but wear-leveling and write amplification are never perfect. Giving any specific numbers for endurance is hard because every drive behaves differently and users have different workloads, but it's unlikely for a light consumer workload to see more than 10GiB of writes per day. That's 3,650GiB per year, which is only 1.4% out of 256,000GiB. In the real world NAND writes will be bigger than host writes but even with a write amplification factor of 10x, you will only end up writing 36,500GiB each year and exhausting ~143 P/E cycles out of the available 1,000. In other words, it would take roughly seven years for you to wear out the NAND.
| SSD Lifetime Estimation | ||||
| NAND | MLC—3K P/E Cycles | TLC—1K P/E Cycles | ||
| NAND Capacity | 128GiB | 256GiB | 128GiB | 256GiB |
| Writes per Day | 10GiB | 10GiB | 10GiB | 10GiB |
| Write Amplification | 10x | 10x | 10x | 10x |
| Total Estimated Lifespan | 10.5 years | 21.0 years | 3.5 years | 7.0 years |
For the 120GB Samsung 840, the lifespan is half of the 250GB model but we are still talking about years. Samsung doesn't offer a 60/64GB Samsung 840, although that makes sense as it wouldn't be hard to wear that out in less than three years, which is the warranty Samsung gives to the 840 SSD.
DSP to the Rescue
However, there is actually more to SSD endurance than just P/E cycles and write amplification. There has been a lot of talk lately about digital signal processing (DSP) in the industry, which is supposedly the solution for lower endurance NAND.
The basic idea behind DSP is very simple: you read changes in voltages and adapt to the changes. As I mentioned in the previous page, the voltages change as the NAND wears out and if your controller can't adapt to the changes, you'll be stressing the NAND even more. Each time you're trying to program or erase the cell, you are wearing it out, so you don't even have to succesfully program or erase the cell to cause damage. That's why the guess and test process for writing to NAND is so harmful; it may take multiple tries and each try will wear out the NAND even more.
Graphical presentation of a change in voltage state
However, if your controller can read the changes in program and erase voltages, you will know what voltages to use to program/erase the cell. 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.
Again, it's hard to give out any specific numbers of DSP usefulness in real world, but for example STEC is claiming that their CellCare technology can extend the endurance of regular 3K P/E cycle MLC up to as much as 60K. I've heard unofficial figures as high as 100K for some companies' DSPs, but I would take all figures with a grain of salt until they are tested by a third party. Either way, even if a good DSP is only able to double the endurance of NAND, it's a huge deal as we move to even smaller process nodes and possibly even more bits per cell.
Facebook
Twitter
RSS
86 Comments
View All Comments
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
Great Drive , but if you have memory problems click here ----> http://www.billatkinson.net/evo