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Thread: Linux 3.10 Kernel Integrates BCache HDD/SSD Caching

  1. #1
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    Default Linux 3.10 Kernel Integrates BCache HDD/SSD Caching

    Phoronix: Linux 3.10 Kernel Integrates BCache HDD/SSD Caching

    After being in development for more than one year, BCache was finally merged on Wednesday into the mainline Linux kernel code-base. BCache serves as an SSD caching framework for Linux by offering write-through and write-back caching through a newly-exposed block device...

    http://www.phoronix.com/vr.php?view=MTM2ODM

  2. #2
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    doesnt writing and above all rewriting shorten an SSDs life time?

  3. #3
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    Quote Originally Posted by jakubo View Post
    doesnt writing and above all rewriting shorten an SSDs life time?
    It does. But it shouldn't really be an issue anyway - in most cases, you'd be prepared to replace a drive which is out of warranty (3-5 years) anyway.

  4. #4
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    Can i use an HD as a cache for network filesystems?

  5. #5

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    Quote Originally Posted by kokoko3k View Post
    Can i use an HD as a cache for network filesystems?
    thats a different sort of problem. bcache assumes that the backing device never gets modified outside bcache.

    a network file system may be receiving modifications from other clients, so the cache needs to either have all these changes broadcast to it, or to do some checking.

  6. #6
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    @jakubo
    Bcache doesn't wear out SSDs, it just writes entire cells at once and garbage collects them. There is no rewriting, it looks like a log-structured filesystem to the SSD.

    @kokoko3k
    Use FSCache for HDD caching of network filesystems.

  7. #7
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    Quote Originally Posted by ssam View Post
    thats a different sort of problem. bcache assumes that the backing device never gets modified outside bcache.

    a network file system may be receiving modifications from other clients, so the cache needs to either have all these changes broadcast to it, or to do some checking.
    That being said, i bet it would work for NBD devices or filesystem images for virtual machines on a networked share, since that shouldn't happen with them.

  8. #8
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    If the cache is an HDD, bcache would throttle it the first time it seeks, ignore it for streamed io, and generally keep it empty. You can tune or disable both features, at the risk of making things slower. HDDs need a lot of readahead which bcache has no reason to do.
    There are plenty of other options when no SSD is involved. Bcache is flexible with respect to backing devices, but it must have an SSD to cache to.

  9. #9
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    Quote Originally Posted by jakubo View Post
    doesnt writing and above all rewriting shorten an SSDs life time?
    Technically... yes. But they are generally pretty good. I know most new Intel ones have the guideline of "10Gbs of data, a day, everyday, for 5 years." Is when it will die. And even then I think it just goes into Read-Only mode instead of dying completely, so you can still get your data off. Also most of the time you're looking to replace the drive anyway before that time limit kicks in. I know the SSD in my laptop will be replaced in a year and a half or so when I get a new laptop, so im not really worried about it.

  10. #10
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    I currently have root on ssd and home on hdd. Would putting it all on hdd and using bcache be faster?

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