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    SubjectRe: [GIT] Bcache version 12
    On Fri, Sep 9, 2011 at 11:45 PM, Kent Overstreet
    <> wrote:
    > bcache, n.: a cache for arbitrary block devices that uses an SSD
    > It's probably past time I started poking people to see about getting
    > this stuff in. It's synced up with mainline, the documentation is for
    > once relatively up to date, and it looks just about production ready.
    > Suggestions are more than welcome on how to make it easier to review -
    > it's entirely too much code, I know (near 10k lines now). I'll be
    > emailing the patches that touch other parts of the kernel separately.
    > Short overview:
    > Bcache does both writethrough and writeback caching. It presents itself
    > as a new block device, a bit like say md. You can cache an arbitrary
    > number of block devices with a single cache device, and attach and
    > detach things at runtime - it's quite flexible.
    > It's very fast. It uses a b+ tree for the index, along with a journal to
    > coalesce index updates, and a bunch of other cool tricks like auxiliary
    > binary search trees with software floating point keys to avoid a bunch
    > of random memory accesses when doing binary searches in the btree. It
    > does over 50k iops doing 4k random /writes/ without breaking a sweat,
    > and would do many times that if I had faster hardware.

    Does it consider the raid5/6 write hole in what it caches? Guess I
    need to take a look at the code, but just wondering if it considers
    the need to maintain a consistent strip when writing back to raid5/6
    array, or would there still be a need for a separate driver/region of
    the SSD for caching that data.

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