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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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