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
xdrol - Monday, October 8, 2012 - link
You sir need to learn how SSDs work. Static data is not static on the flash chip - the controller shuffles it around, exactly because of wear levelling.name99 - Tuesday, October 9, 2012 - link
"I think Kristian should have made this all more clear because too many people don't bother to actually read stuff and just look at charts."Kristian is not the problem.
There is a bizarre fraction of the world of tech "enthusiasts" who are convinced that every change in the world is a conspiracy to screw them over.
These people have been obsessing about the supposed fragility of flash memory from day one. We have YEARS of real world experience with these devices but it means nothing to them. We haven't been screwed yet, but with TLC it's coming, I tell you.
The same people spent years insisting that non-replacable batteries were a disaster waiting to happen.
Fifteen years ago they were whining about the iMac not including a floppy drive, for the past few years they have been whining about recent computers not including an optical drive.
A few weeks ago we saw the exact same thing regarding Apple's new Lightning connector.
The thing you have to remember about these people is
- evidence means NOTHING. you can tell them all the figures you want, about .1% failure rates, or minuscule return rates or whatever. None of that counts against their gut feeling that this won't work, or even better an anecdote that some guy some somewhere had a problem.
- they have NO sense of history. Even if they lived through these transitions before, they cannot see how changes in 2000 are relevant to changes in 2012.
- they will NEVER admit that they were wrong. The best you can possibly get out of them is a grudging acceptance that, yeah, Apple was right to get rid of floppy disks, but they did it too soon.
In other words these are fools that are best ignored. They have zero knowledge of history, zero knowledge of the market, zero knowledge of the technology --- and the grandiose opinions that come from not actually knowing any pesky details or facts.
piiman - Tuesday, February 19, 2013 - link
Then stick with Intel not because they last longer but they have a great warranty.(5 years) My drive went bad at about 3.5 years and Intel replaced it no questions asked and did it very quickly. I sent it in and had a new one 2 days after they received my old one. great service!GTRagnarok - Monday, October 8, 2012 - link
This is assuming a very exaggerated amplification of 10x.Kristian Vättö - Monday, October 8, 2012 - link
Keep in mind that it's an estimation based on the example numbers. 10x write amplification is fairly high for consumer workloads, most usually have something between 1-3x (though it gets a big bigger when taking wear leveling efficiency into account). Either way, we played safe and used 10x.Furthermore, the reported P/E cycle counts are the minimums. You have to be conservative when doing endurance ratings because every single die you sell must be able to achieve that. Hence it's completely possible (and even likely) that TLC can do more than 1,000 P/E cycles. It may be 1,500 or 3,000, I don't know; but 1,000 is the minimum. There is a Samsung 830 at XtremeSystems (had to remove the link as our system thought it was spam, LOL) that has lasted for more than 3,000TiBs, which would translate to over 10,000 P/E cycles (supposedly, that NAND is rated at 3,000 cycles).
Of course, as mentioned at the end of the review, the 840 is something you would recommend to a light user (think about your parents or grandparents for instance), whereas the 840 Pro is the drive for heavier users. Those users are not writing a lot (heck, they may not use their system for days!), hence the endurance is not an issue.
A5 - Monday, October 8, 2012 - link
Ah. I didn't know the 10x WA number was exceedingly conservative. Nevermind, then.TheinsanegamerN - Friday, July 5, 2013 - link
3.5 years is considering you are writing 36.5 GB of data a day. if the computer it is sitting in is mostly used for online work of document editing, youll get far more. the laptop would probably die long before the ssd did.also, this only apples to the tls ssds. mlc ssds last 3 times longer, so the 840 pro would be better for a computer kept longer than 3 years.
Vepsa - Monday, October 8, 2012 - link
Might just be able to convince the wife that this is the way to go for her computer and my computer.CaedenV - Monday, October 8, 2012 - link
That is how I did it. My wife's old 80GB system drive died a bit over a year ago, and it was one of those issues of $75 for a decent HDD, or $100 for an SSD that would be 'big enough' for her as a system drive (60GB at the time). So I spent the extra $25, and it made her ~5 year old Core2Duo machine faster (for day-to-day workloads) than my brand new i7 monster that I had just build (but was still using traditional HDD at the time).I eventually got so frustrated by the performance difference that I ended up finally getting one for myself, and then after my birthday came then I spent my fun money on a 2nd one for RAID0. It did not make a huge performance increase (I mean it was faster in benchmarks, but doubling the speed of instant is still instant lol), but it did allow me to have enough space to load all my programs on the SSD instead of being divided between the SSD and HDD.
AndersLund - Sunday, November 25, 2012 - link
Notice, that setting up a RAID with your SSD might hinder the OS to see the SSDs as SSD and not sending TRIM commands to the disks. My first (and current) gamer system consists of two Intel 80 GB SSD in a RAID0 setup, but the OS (and Intel's toolbox) does not recognize them as SSD.