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back to article TLC NAND could penetrate biz with flash-to-flash backup

Violin co-founder and CTO Jon Bennett identified a potential enterprise role for three-level cell (TLC) flash at VMworld Barcelona today: flash-to-flash backup. TLC is currently seen as pure consumer technology. The first TLC NAND SSD has been announced by Samsung. But TLC NAND has a short working life, with 500 - 750 phase/ …

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  1. Jim O'Reilly
    Holmes

    Return of the Data

    At the current state-of-the-art, the idea of yet another storage tier using TLC is worth discussion, but it isn't a feasible play yet. Any backup device has to guarantee long-term retention of the data, and a low error rate on that data when it is restored. This is especially true of highly de-duplicated data.

    Looking at restore, there are a couple of modes involved. Restoring a single file is a random access event. While flash will be faster, the overhead of loading programs, selecting files etc will swamp the speed difference. In batch restores, the issue is sequential throughput, where flash has a much smaller edge over HDD. Here, the cost per GB of HDD is so low compared with flash that extra drives are affordable, and the backup array can thus be lifted up to flash levels and still be cheaper.

    Flash backup isn't a near-term proposition, except perhaps in Mil-spec applications. Ultra-rugged HDD modules for distributing movies to theaters could be replaced by flash, but the capacities involved probably don't require TLC.

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    1. Oninoshiko
      Reply Icon

      data for movies

      It might not REQUIRE TLC, but if the costs per meg are lower then MLC (why are "Triple Level Cells" not "Multi Level Cells?" Grr.) it would make sense to use it for that application. Although I'm not really sure why they would use flash as opposed to a write-once medium.

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      1. Jim O'Reilly
        Reply Icon

        Re: data for movies

        Movies range up to 250GB for the 3D format. They use a very high resolution 4K graphics image. The result is they don't fit Blu-Ray disks, and the use of multiple disks would be a nightmare to manage. Currently movies go out on HDDs in special rugged cases. If the HDD were replaced with SSD, the cost would probably be close, since the cases are very expensive.

        They are typically shipped via common carrier, and HDDs do get damaged. This can be a potential hit for theaters since only one copy is shipped which runs from a central server. Likely SSD would be more reliable.

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  2. Mephistro
    Gimp

    Great idea!

    Incremental backups on unreliable media. What could possibly go wrong?

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  3. jcrb

    the drives might be affordable, if only you didn't need so many..

    Jim,

    The point you are missing is that for a disk backup system to have as much throughput at a 3U flash array you are probably looking at anywhere from 1/2 to a whole rack of disks. So apart from the issue of the floor space consumed you will be buying so much more capacity than needed even if you buy small disks that I don't think it will turn out to be as cheap as you think it is.

    Particularly since the idea is just to keep the backups you are likely to need to restore quickly, which would be last night, or the last time your did a full backup of your database, etc which shouldn't be that far back. So again totally over buying the capacity is going to make the disk system a lot less attractive.

    Jon

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