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.

Lower Endurance - Why? The Samsung SSD 840
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  • mapesdhs - Friday, October 12, 2012 - link


    I have SCSI disks that are more than 20 years old which still work fine. :D

    Ian.
    Reply
  • MarkLuvsCS - Monday, October 08, 2012 - link

    Considering Write Amplification has been significantly reduced compared to the initial SSD tech, I don't believe it's going to be a problem for the consumer market. Google xtremesystems Write Endurance to see a Samsung 830 256gb with 3000 P/E still running at 4.77 PETABYTES.That page also shows you other brands and how they fare. I would trust Samsung wouldn't put this tech to use without truly understanding how it would pan out.

    That is why the worry of the 1000 P/E 840 vs 3000 P/E 830 is overblown. Either way you have little to worry about with Samsung's controllers causing any fuss unlike Other CompanieZ.
    Reply
  • Kjella - Monday, October 08, 2012 - link

    Not giving one fsck about wearing out the SSD I burned through a 10k-rated SSD in 1.5 years. Now with fairly normal SSD usage - a standard Win7 desktop with torrents etc. on other drives - I'm down to 57% health and looking at 3 years 10 months on a 5K-rated drive. I don't know exactly what is eating it but I'm guessing every log file, every time MSN or IRC logs a line of chat, every time something is cached or whatever it burns write cycles. I feel the official numbers are vastly *overstating* the actual lifespan, not understating it. TLC with 1K writes? Not in my machine, no sir. Reply
  • madmilk - Monday, October 08, 2012 - link

    There's no way MSN/IRC can burn through an SSD in 1.5 years since they're all text. You must be doing something unusual, or at least your computer is without you knowing it. A good idea would be to open up Task Manager, and select the columns that count the number of bytes written by various programs. Maybe then you can find the source of your problem. Also make sure you have defragmentation off, and sufficient RAM so you're not constantly hitting the pagefile. Reply
  • piiman - Tuesday, February 19, 2013 - link

    Better yet put the page file on a different drive and also move your temp folders to a different drive. Reply
  • Notmyusualid - Tuesday, October 09, 2012 - link

    Absolutely hilarious ending there pal... I wonder how many people got it!

    I got burned by them on a couple of drives, and promptly dumped them on some well-known auction site, sold as-is.
    Reply
  • creed3020 - Tuesday, October 09, 2012 - link

    I see what you did there ;-)

    Great review Kristian! I'll be looking at this drive as option for a new office PC I am building.
    Reply
  • B3an - Monday, October 08, 2012 - link

    Did you people even bother to read?? Because you're conveniently missing out the important fact in this article that you'd have to write 36.5TiB (almost 40TB) a year for it to last 3.5 years. I know for a fact that the average consumer does not write anywhere near that much a year, or even in 3 years. If anyone even comes close to 40TB a year they would be using a higher-end MLC SSD anyway as they would surely be using a workstation.

    Most consumers don't even write 10GB a day, so at that rate the drive would easily last OVER 20 years. But of course it's highly likely something else would fail before that happens.

    You're also forgetting out DSP which is explained in this article as well. That can also near double the life.

    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.
    Reply
  • futrtrubl - Monday, October 08, 2012 - link

    Granted the usual use cases won't have so much data throughput. However those same usual use cases have the user filling 3/4 of the drive with static data (program/OS/photo archive etc) reducing the drive area it's able to wear level over. So that 20 years again becomes 5 years.

    Also the 1000PE cycle stat means that there is a 50% chance for that sector to have become unusable by that time (ignoring DSP).

    I'm not saying that TLC is bad, and I am certainly not saying this drive doesn't have great value. I'm just saying that we shouldn't understate the PE cycle issue.
    Reply
  • xdrol - Monday, October 08, 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. Reply

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