A week ago Samsung acknowledged the existence of the read performance bug in the SSD 840 EVO and I just received a note that the fixed firmware is in validation process and is expected to be released to the public on October 15th. Unfortunately I don't have any further details about the bug or the fix at this point, or whether the update is coming to the 'vanilla' SSD 840 and OEM models, but I hope to get more details as the public release gets closer, so stay tuned.

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  • Solid State Brain - Saturday, September 27, 2014 - link

    A non-EVO 840 250GB in one of my systems is showing this issue on old static data, according to LBA scan read benchmarks. However the user who is actively using that PC didn't notice any significant slowdown. Reply
  • arrc - Monday, October 06, 2014 - link

    What are your benchmark results? I'm also on a 840 500GB running SATA II, and I'm getting horrible benchmark results.. Reply
  • Solid State Brain - Saturday, September 27, 2014 - link

    The latest firmware by Samsung for their SSD was released on March '14 for 840 and 840 Pro models, so there's little reason to believe they won't release additional ones to fix this issue. The latest firmware for 840 EVO drives is still the original one issued on December '13. Reply
  • bsim500 - Saturday, September 27, 2014 - link

    So what does the new firmware do exactly? Simply move old data around much more often? That's going to kill TLC endurance (which is already less than 1/3rd that of everyone else's MLC drives in endurance tests).

    I think Samsung have made a huge mistake with TLC if its data retention really is that bad. It's not as if the TLC drives are significantly cheaper than MLC, which apparently was supposed to be the prime advantage of TLC (lower cost)? Where I live, a 512GB Samsung Pro (high endurance MLC) is almost £240. A buggy 512GB Samsung 840 EVO (low endurance TLC) is around £150-155. But a perfectly working 512GB Crucial MX 100 (high endurance MLC) is around £145. Total no-brainer...
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  • Death666Angel - Saturday, September 27, 2014 - link

    "I think Samsung have made a huge mistake with TLC if its data retention really is that bad."
    Is it, though? I haven't dived into devouring forums posts about this stuff, But on my main tech news site, no one said that the data was lost because of this bug, only that older files were getting read very slowly. And I haven't only found that to be on the Evo drive, not the vanilla 840. At this point in time, it seems prudent to go with the MX100 (though not having public bugs at this stage does not mean it is bug free, see 840 Evo :P). But to draw any other conclusions from this (TLC is bad, data retention is bad) seem premature and not based in the facts presented so far.
    Reply
  • hojnikb - Saturday, September 27, 2014 - link

    Well, TLC is inherently worse on pretty every aspect compared to MLC, so there is some truth in that, even if firmware proves to fix the issues. Reply
  • Death666Angel - Saturday, September 27, 2014 - link

    Not really a point to anything I wrote about. The TLC drive I bought (500GB 840) was the cheapest 500GB SSD at the time, so TLC saved me money. The performance was better than most MLC drives at the time, except ones much more expensive. And I specifically talked about the data retention aspect of TLC, as that was what the OP mentioned. So whatever "truth" you are referring to, it alludes me. Reply
  • bsim500 - Saturday, September 27, 2014 - link

    Well others with "vanilla" 840's have indeed been complaining about the bug too in multiple forums, so it's definitely not limited to the EVO. I don't know for sure if it is TLC, but so far it only seems to affect the Samsung TLC drives (840 & 840 EVO). The MLC drives (840 Pro and older 830 (of which I own one)) are completely unaffected. It might be the TLC itself losing charge causing heavy error correction to slow it down, or it might be a combination of TLC + 19nm process or it might be firmware specifics for TLC (from what I remember of Anand's review, Samsung's dedicate a small portion of each TLC NAND die as an SLC write buffer, ie, an extra layer of complexity over MLC drives):-
    http://www.anandtech.com/show/7173/samsung-ssd-840...

    Either way, if it's just a "firmware speed bug", then it's a pretty big bug to miss, but if "data loses charge far quicker than expected causing slowdown due to error correction" is an unforeseen side-effect of small-process TLC, then "move data around more" firmware is really more of a workaround than a "fix". In any case, I can't understand why the Samsung Pro MLC's are so much more expensive compared to everyone else's MLC drives?
    Reply
  • Solid State Brain - Saturday, September 27, 2014 - link

    Since rewriting the data (for example with a defrag) apparently temporarily solves this issue, all points to 840/840 EVO-specific bugs with wear leveling algorithms, which are already supposed to do that in the background during write operations. Every SSD in order to minimize lifetime wear is supposed to use all NAND cells more or less uniformly, and if TLC-equipped Samsung SSDs aren't doing that, they actually are wearing up faster, not slower as some people here are writing. Reply
  • Kristian Vättö - Saturday, September 27, 2014 - link

    Not exactly correct. Wear leveling actually causes additional wear on the NAND because it rewrites data that has already been written. Samsung's wear leveling in the 840 and 840 EVO seems to be very passive to avoid extra NAND writes, which is why even heavy writing to the drives won't recover performance of old data as the drive doesn't seem to move static data around. At some point it definitely should, but it could very well be that the firmware is designed to wear out (~800-900 P/E cycles) the empty blocks first before it touches blocks with static data because that results in less overall wear than constant wear leveling would. Reply

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