Re: MD/DM and barriers (was Re: [patch] ext2/3: documentconditions when reliable operation is possible)

[Pavel Machek]

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 :-(.

									Pavel
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