Daniel Lemire's blog

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Solid-state drives: when external memory becomes as fast as internal memory

6 thoughts on “Solid-state drives: when external memory becomes as fast as internal memory”

  1. Harold Jarche says:

    Zonbu (linux based and much cheaper) uses a solid state drive as well, though you only have 4 GB onboard.

  2. Kevin Burton says:

    The biggest barrier to entry is the write speed.

    To date most of the SSDs we’ve looked at have lied about their write speed by saying the drive can do 100MB/s but when you benchmark it can only do about 20MB/s write throughput. It can still do 100MB/s reads but that’s not too great if you’re 100% write bound like we are.

    We’re going to be getting some to play with shortly and I’m very excited by this 🙂

  3. Daniel Lemire says:

    Thanks for the comment Kevin….

    Are those sequential writes… as in… you need to dump one large contiguous stream of data… or is it random access like building an external memory hash table?

    SSD are apparently very bad at random writes… but they do ok at sequential writes… because of their data block structure…

  4. Kevin Burton says:

    Dan,

    Well, *some* of the SSDs are bad at random writes.

    HDDs are perfectly good at sequential writes. The HDDs we’re using now are GREAT at them. Nearly 100MB/s.

    More modern SSDs can do fine at random writes. The mtron SSDs can so fully random 4k writes @ 80MB/s.

    In fact, the prime reason we’re going with SSD is that they can do random writes at this speed.

    In fact, they’re great at random reads too.

    You can do fully random 4k reads at up to 100MB/s 🙂

    In fact, you can read the whole drive, randomly, in 32 seconds 🙂

  5. Daniel Lemire says:

    Thanks, for the comments.

    > Well, *some* of the SSDs are bad at random writes.

    My impression was that the current breed of high-capacity SSDs are bad at random writes.

    > HDDs are perfectly good at sequential writes. The HDDs we’re using now are GREAT at them. Nearly 100MB/s.
    > More modern SSDs can do fine at random writes. The mtron SSDs can so fully random 4k writes @ 80MB/s.

    Wow. I find it odd that you have nearly no penalty for the random writes. What is the trade-off? Cost? Capacity?

    > In fact, they’re great at random reads too.
    > You can do fully random 4k reads at up to 100MB/s 🙂
    > In fact, you can read the whole drive, randomly, in 32 seconds 🙂

    So the drive has a 4 GB capacity?

  6. Kevin Burton says:

    Read this:

    http://www.nextlevelhardware.com/storage/battleship/

    and this:

    http://feedblog.org/2007/12/13/ssd-vs-memory-the-end-is-nigh/

    These drives can do a HIGH number of iops which is why they can do the high write rate.

    The trade off is capacity.

    The drives we’re looking at are only 32GB.

    We should have the drives this week so I’m hoping to have mysql benchmarks soon.

    Kevin