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    SubjectRe: MD/DM and barriers (was Re: [patch] ext2/3: document conditions when reliable operation is possible)
    On Thu 2009-08-27 12:54:05, Jeff Garzik wrote:
    > On 08/27/2009 09:10 AM, Ric Wheeler wrote:
    >> One thing that does need fixing for some MD configurations is to stress
    >> again that we need to make sure that barrier operations are properly
    >> supported or users will need to disable the write cache on devices with
    >> volatile write caches.
    > Agreed; chime in on Christoph's linux-vfs thread if people have input.
    > I quickly glanced at MD and DM. Currently, upstream, we see a lot of
    > if (unlikely(bio_barrier(bio))) {
    > bio_endio(bio, -EOPNOTSUPP);
    > return 0;
    > }
    > in DM and MD make_request functions.
    > Only md/raid1 supports barriers at present, it seems. None of the other
    > MD drivers support barriers.

    Not even md/raid0? Ouch :-(.

    (cesky, pictures)

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