Messages in this thread | | | Date | Thu, 27 Aug 2009 12:54:05 -0400 | From | Jeff Garzik <> | Subject | MD/DM and barriers (was Re: [patch] ext2/3: document conditions when reliable operation is possible) |
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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.
DM has some barrier code... but the above code was pasted from DM's make_request function, so I am guessing that DM's barrier stuff is incomplete and disabled at present.
I've been mentioning this issue for years... glad some people finally noticed :)
Jeff
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