Samsung SSD 840 (250GB) Review
by Kristian Vättö on October 8, 2012 12:14 PM EST- Posted in
- Storage
- SSDs
- Samsung
- Samsung SSD 840
- TLC
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.
82 Comments
View All Comments
KAlmquist - Tuesday, October 09, 2012 - link
One thing I've been wondering is what voltage the controller uses. I can't identify every component on the board, but I don't see anything that looks like a voltage regulator. It seems kind of crazy to run a chip with three processor cores at 5 volts, but I guess it's possible. ReplyDeath666Angel - Tuesday, October 09, 2012 - link
Loved the review. I'm really looking forward to more data on the DSP usefulness inside SSDs, could be a huge advantage (though I don't worry about going through my P/E cycles at home).With SSDs, we are at a point similar to GPUs and CPUs where I don't understand upgrading from generation to generation. Unless you have a very specific usage case and can make great use of the better speed (video/picture editing or something equally I/O intensive), I don't think a 840 Pro will feel that much faster than a 830.
I'm still rocking a first gen Agility 60GB in my (ULV) notebook and a Vertex2 120GB in my desktop and they feel plenty fast, especially those times when I'm at a friends PC with only mechanical storage.
I might upgrade to a 830 or 840 (non Pro) when the prices have dropped for the 830 or stabilized for the 840 (I don't like paying for launch pricing). :D
And I finally got my brother to go to SSD storage, too! He'll either get a 512GB 830 or 2x256. Does anyone know why 256GB usually has the best price/GB instead of the 512GB drives? Considering the cost for casing, PCB, controller etc. stays the same, I would expect the 512GB to have better pricing/GB. Do they need to go with more dense packages which are more expensive? Reply
name99 - Tuesday, October 09, 2012 - link
I agree completely.I've said before that the current emphasis on performance over everything else is as stupid as Intel's Pentium4 philosophy. Devices have to become more balanced if they want to sell better.
In particular the current atrocious write power draws for these devices mean that they will not sell in the external drive market --- they can't be fully powered by USB2 and
- no-one wants a drive that needs two USB connections because it's clumsy and it uses up limited USB slots
- saying it can be fully powered by USB3 is not good enough because, for the near-term future, people want to share drives between USB2 and USB3 computers.
Of course MOST, but not all, the external drive market is about capacity, not speed. However each time SSD capacity doubles, a larger portion of the external drive market makes sense; AND power is not only an issue for the external market. The higher you set your peak power draw, the less your flash appeals to Ultrabook manufacturers.
Just remember Pentium 4 and its power draw, and compare to Intel trying to get Haskell to run at <10W nowadays. Balance matters, and current flash manufacturers seem to be far too unbalanced compared to the requirements of most users.
(It would be fascinating, for example, if we learn that the flash in the next round of iOS devices, or even MacBooks, was designed in-house by Apple because they were not satisfied with the power vs performance choices that were being made by the major flash manufacturers. Remember --- Apple bought Anobit...) Reply
moadip - Tuesday, October 09, 2012 - link
does the 830/840 family support AES encryption? Want to buy one of those but there is no official word on any support for this. Is anyone of you guys/girls using them in that way? ReplyKristian Vättö - Tuesday, October 09, 2012 - link
840 and 840 Pro both support 256-bit AES encryption Replymoadip - Tuesday, October 09, 2012 - link
what about the 830? ReplyKristian Vättö - Tuesday, October 09, 2012 - link
I'm not 100% sure but as far as I know, only the OEM/enterprise version (i.e. PM830) supports encryption, the consumer 830 doesn't. ReplyMrSpadge - Tuesday, October 09, 2012 - link
What an amazingly well balanced drive! Currently it's more expensive than the 830 at similar capacities, but as soon as 21 nm yield ramps up (and prices are adjusted) this will probably be one of the best or maybe the best consumer SSD on the market. ReplyiCrunch - Tuesday, October 09, 2012 - link
Thanks for another tremendous AnandTech review! You guys are insane! ;-)I own a 256GB Samsung 830 as part of my Retina MBP and I must say, I'm blown away! My first SSD was an Intel X25-M G1 80GB and through the years, I've had the fortune to own several solid state drives, including the OWC Mercury Extreme Pro 6Gbps, a couple of Intel 520's in RAID 0, the Samsung 470 as well as pre-470 Samsung OEM models. Thanks to this review, I'll be going for the 840 Pro as soon as soon as I can justify getting another desktop or laptop. Decision made!
I'm used to high SSD pricing, so if the 840 Pro 256GB will be going for $250 or less, count me in. If the downward trend of SSD prices really does continue, or, even better, if a breakthrough drive like the 840 series with its less expensive TLC NAND appears to be, I'd love to start getting 512GB drives. Black Friday, here we come... Reply
chrcoluk - Tuesday, October 16, 2012 - link
I have a 830 and am happy with it but it does have a weakness on high threaded i/o and random writes, it seems they have address this on the 840 pro which seems a bug fixed 830. However I have noticed the huge price premium on the 840 pro. Seems samsung have finally realised they can sell based on their reputation as they are in the same league as intel for reliability above the likes of OCZ who are trash. This day was inevitable. The basic 840 is to cater for the lower price market to try and keep hold of customers who wont pay more and time will tell if it works out. My observation so far is the basic 840 still costs more than the 830s, for me thats a no go, whilst it does have the newer controller which gives higher random writes, the random writes arent slow enough on my 830 for it to be an issue, its not noticeable. So for me its about reliability and the 830 I expect with its superior nand to be be the better product yet is still cheaper. If I won the lottery I would buy some 840 pros, but otherwise its 830s for me.As for write wear, my browsers alone are writing 10s of gigs of data a day, I moved my browser temp data folders to a ramdisk. Everytime someone views a youtube video eg. it writes to the browser cache even tho its a stream. Same if you download files, they written to the temp folder before the download folder. I feel anandtech solely focusing on performance are not been responsible they need to warn people of the risks of using TLC. Reply