SSDs no more reliable than hard drives

SSDs no more reliable than hard drives

Summary: The marketers have pounded the "no moving parts" line to convince you that SSDs must be more reliable than hard drives. But it isn't true. Here's why.

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TOPICS: Hardware
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A great piece of investigative reporting in Tom's Hardware on SSD reliability today. Writer Andrew Ku talked to users of more than 160,000 SSDs and tabulated their responses. It is the largest scale study of SSDs ever - other than what vendors keep close to the vest.

It is a long report and if you are professionally responsible - or just really curious - about SSDs I urge you to read it right now. But if you want the high points - and some advice - read on.

The sample Mr. Ku spoke to a number of users, including some who requested anonymity, who ranged in sample size from less than 100 SSDs to over 150,000 units. Respondents included NoSupportLinuxHosting.com, InterServer.net, Steadfast Networks, Softlayer and - with 155,000 SSDs - ZT Systems. In addition he spoke to a number of other sources at supercomputer centers, research groups and other end-users.

Almost all the drives in the study are Intel drives, because they are currently the most trusted SSDs. This puts the spotlight on Intel, but presumably other drives would fare no better and in some cases much worse. With their Micron JV and their own flash translation layer (FTL), Intel is one of the few vertically integrated SSD vendors. And as one of the world's largest mobo vendors, they arguably have the most systems-level expertise of any SSD player.

The issues Comparing the reliability of a 50 year old technology against a 5 year old one isn't easy. Both are moving targets, the use cases are different, and among SSD vendors the reliability is all over the map. But in my view here are some of the key issues:

  • Failure rates. Storage vendors routinely claim that ≈50% of all returned drives are NTF - no trouble found - when tested. I take a consumer perspective: if it isn't working it's failed. But vendors have a point: they only control their piece of the puzzle, but get blamed for the whole thing. Life can be unfair.
  • Substitution effect. If I replace 5 drives with 1 SSD, what happens to reliability - especially if the 5 drives are in a RAID stripe?
  • Age. Few of the SSDs in this study are over 2 years old, while lots of HDDs are. We know that HDD failure rates increase with age, especially after 3 years, and we don't know how SSDs will age.
  • Endurance. End-users worry about the fact that NAND flash is spec'd for a limited number of writes, but for most that isn't the problem. It is the other failure modes that bite you.
  • Entropy. It doesn't matter what technology we use, the universe hates your data and always will.

The Storage Bits take All SSDs do is replace a hard drive's head disk assembly - the platters and heads - with a lot of flash chips. The rest of the stuff is the same - and that stuff accounts for about half of all drive failures. So the best we can expect is that SSDs could be twice as reliable.

But flash isn't that reliable either, especially as feature sizes shrink. Few know that it takes ≈20 volts to write NAND flash, which is a lot when insulators are molecules thick. Entire plane failures on flash die are common.

And those are only the obvious problems.

Bottom line: treat your SSDs as you do hard drives. Back up regularly. Use redundancy if uninterrupted service is the goal.

And know that you are only buying performance - not reliability.

Comments welcome, of course.

Topic: Hardware

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  • RE: SSDs no more reliable than hard drives

    Do the SSDs suffer from a limited number of read/writes like USB sticks do?
    LoverockDavidson
    • Yes, they do...

      @LoverockDavidson It used to be fairly low - like 100,000 writes - but it's up over a milion now.
      TheWerewolf
      • Not entirely accurate...

        @TheWerewolf The more reliable and MUCH more expensive SLC can do about 100,000 write cycles, however the stuff used in most consumer rated products from Intel and others (the 160GB drives for $250ish) use MLC based flash which maxes at 10,000 write cycles.

        Also, as the process shrinks this gets worse not better. I believe the latest 25nm MLC chips achieve about 3,000 write cycles (at least that is the figure I have seen thrown around, that may be for something even smaller, I reserve the right to be wrong here). What does give flash more life is much better write algorithms to spread the pain of a write cycle around to all of the flash blocks equally.
        Rabayn
      • RE: SSDs no more reliable than hard drives

        @TheWerewolf While I cannot disagree with this article, my Kings<a href="http://www.tran33m.com/vb/">t</a>on SSD has experienced (probably) more read/writes than most personal users have (at 1 year of useage). I play with my PC A LOT. I am constantly adding and re<a href="http://vb.maas1.com/">m</a>oving apps and along with the regular background tasks, including BOINC, my PC runs 24/7. My SSD has yet to hiccup. I will not be returning to platters for use as my OS drive.
        alasiri
    • RE: SSDs no more reliable than hard drives

      @LoverockDavidson
      Yes they do, but the limitations aren't important for the huge majority of applications. A low-spec 80GB MLC SSD with 3,000 write cycles can write 10GB/day for 18 years. That works for me.
      R Harris
      • RE: SSDs no more reliable than hard drives

        @R Harris
        Thanks, didn't realize they would last that long.
        LoverockDavidson
      • But the problem with SSDs is that they just die the same way as flash ...

        @LoverockDavidson: ... drives.

        <b>Totally out of the blue, for now apparent reason and no hint from S.M.A.R.T. data.</b>

        I mean that I am amused that anyone might think that SSDs are "more reliable" just because they do not have moving parts.

        (Mind you, in HDDs' deaths moving parts are actually one of the last reasons; usually, it is magnetic layers that starts to deteriorate.)
        DDERSSS
      • RE: SSDs no more reliable than hard drives

        I use SSDs in my netbooks because, since they have no moving parts, they are far more reliable when dropped from a height such as off of a roof. (I deal with wireless equipment.)

        So there's reliability and there's reliability.

        I use Ubuntu Netbook Remix 10.04 and have set noatime on all the SSDs and no swap partition to avoid the write limits. Not that it's a big issue, but, why tempt fate?

        I have an Acer Aspire One that had the default Linpus on it and its SSD simply disappeared one day. It was there one moment, and gone the next. Failure of an SSD is very abrupt.
        mheartwood
    • RE: SSDs no more reliable than hard drives

      @LoverockDavidson The technical limitations are negigible. However let's take for instance this <strong><a href="http://www.preciolandia.com/ar/discos-rigidos-360-gb-a-500-gb-4o8/deno1.html">500 GB hard drive</a></strong> (<strong><a href="http://www.preciolandia.com/ar/360-gb-a-500-gb-externos-sgh/deno1.html">disco duro portable</a></strong> in spanish) priced at less than 80 bucks in <b><a href="http://www.preciolandia.com/ar/">PrecioLandia Argentina</a></b>. It has 7 years warranty. Now, a <strong><a href="http://www.preciolandia.com/ar/pen-drives-32-gb-o-mas-13g6/deno1.html">32 GB Pen Drive</a></strong> is worth 50 bucks. You divide GB/cost and you tell me what's convenient...<br>You are free to check for <b><a href="http://www.preciolandia.com/br/">prices in Brazil</a>, <a href="http://www.preciolandia.com/cl/">Chile</a> or <a href="http://www.preciolandia.com/ve/">Venezuela</a></b>. The proportion stands.
      preciolandia
      • RE: SSDs no more reliable than hard drives

        @preciolandia What about converting <strong><a href="http://www.sudolar.com">USD (dolar)</a></strong> to Pesos?
        I would love to know the price of <strong><a href="http://www.sudolar.com">dolar hoy</a></strong>.
        sudolar
    • RE: SSDs no more reliable than hard drives

      @LoverockDavidson

      "Comparing the reliability of a 50 year old technology against a 5 year <strong><a href="http://learnviolinonlinehq.com/">learn violin online</a></strong> old one isn???t easy. Both are moving targets, the use cases are different, and among SSD vendors the reliability is all over the map. But <strong><a href="http://glaucomaeyedrops.com/">glaucoma eyes drops</a></strong> in my view here are some of the key issues:"

      And also, I bet the first harddrives from 50 years ago were very unreliable as well! Possibly more than SSD's are nowadays. Give the <strong><a href="http://brighteyesdrops.com/">bright eyes drops</a></strong> SSD's 45 more years, and I assure you that they are working perfectly fine. It's still quite a new technology, remember ;)
      runeklan
  • Beware of new whiz bang technology ...

    New technology breakthroughs are nice, but they usually are not all they are marketed to be. This, most certainly, includes SSDs. Old technology, like hard drives, with all their warts are a known technology and are much more predictable. I have really been tempted by the SSD revolution. However, at this point I am finding it more prudent to spend the extra bucks on premium conventional hard drives for my RAID arrays. I still see the big breakthrough in terms of data integrity as being intelligently redundant and continually checksumming next generation file systems such as ZFS and btrfs. I plan to move to btrfs as soon as online fsck is available from Oracle.
    George Mitchell
  • RE: SSDs no more reliable than hard drives

    I think it would be more precise to say they are less susceptible to fall damage, since they can't physically "crash" like platter drives can.

    "We know that HDD failure rates increase with age, especially after 3 years, and we don?t know how SSDs will age."

    Partially untrue. We do know that they have so many writes, and from that we can make a reasonable guess about when they wear out. We can do a bit of figuring, and I'm sure there's been plenty of lab tests about it.

    "The rest of the stuff is the same - and that stuff accounts for about half of all drive failures."

    Yeah, and that's always kinda confused me - why is it so difficult to make a reliable controller for these things? Why is it that some manufacturers seem to have lots of issues, while others are rock solid? Why do some fail quickly while others outlast the physical components?

    "Entropy. It doesn?t matter what technology we use, the universe hates your data and always will."

    That's what ECC is for. And one of the reasons I often disagree with you - IMO ECC technology is generally doing far better than you give it credit for. It's not perfect, but I think you often exaggerate how much it misses errors.

    And of course a good backup doesn't hurt either :).

    "Bottom line: treat your SSDs as you do hard drives. Back up regularly. Use redundancy if uninterrupted service is the goal."

    I'd agree :). Always a good idea, no matter what the tech. Stuff happens.
    CobraA1
    • RE: SSDs no more reliable than hard drives

      @CobraA1
      ECC does amazing things - and with 4k sectors it does even better - but all error specs are <i>after</i> the ECC and as many retries as the drive supports.

      It's only because the ECC is as good as it is that error specs are as high as they are. And the error specs are probably optimistic.
      R Harris
      • RE: SSDs no more reliable than hard drives

        "but all error specs are after the ECC and as many retries as the drive supports."

        So I've heard. But something else is probably checking the data, because I've dealt with large files of many types with no issues. I'm fairly certain there's some error detection/correction that's doing a better job than you're accounting for - perhaps in one of the busses or in the OS, I dunno, but my current machine has been pretty solid no matter how much I've thrown at it, even with things like zip archives and encrypted files, which are sensitive to bit flips.
        CobraA1
      • RE: SSDs no more reliable than hard drives

        I have to agree with Cobra on this. My experience going back to the mid nineties is that I can't really put my finger on *any* missing data during that period, with one exception. I *suspect*, but can't prove, a bit of data loss from old 100MB Zip disks. But data loss from hard drives? None that I am aware of. And this in spite of several hard drive failures during that period with no backups. I've learned my lesson on that at this point. Hardware RAID, hourly syncs to a non-RAID stand alone mirror, daily syncs to standalone snapshots on dedicated disk going back for three weeks. Quarterly BluRay backups. One can't be too careful, but my experience is that data loss from bit rot is not all that common.
        George Mitchell
      • RE: SSDs no more reliable than hard drives

        @CobraA1, George Mitchell,
        My experience is that most of what is caused by bit rot isn't seen as data loss. Missing DLL? Can't find App? Document formatting borked? Drive not found? Plist corruption?

        There are many failure modes caused by bit rot. If you think hard you may start to remember odd behavior that was unexplained - or outright failures - and those were likely caused by bit rot.
        R Harris
  • RE: SSDs no more reliable than hard drives

    My current OCZ Vertex 3 SSD is driving me nuts. It randomly reboots every night or every other night. My Vertex 1 on the other hand never game me 1 problem. You win some you lose some. The speed of the SSD makes up for the random reboots, since it never reboots when I am using it.
    Bates_
  • RE: Build your own Home Theater PC (HTPC) ... for under $600!

    I just put a SSD in my MacBook a couple of months ago and it's the single best performance upgrade that I've ever made. While SSDs may not be any more reliable, maybe even a little less reliable than spinning disks the speed improvement is well worth it. I think the same applies to SSDs as does to any other data storage solution, backup backup backup!
    jonfleck
  • RE: SSDs no more reliable than hard drives

    At the end of the day one has to realize that if something is going to fail it will.
    msdaniellec