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Bug#584881: Lockups under heavy disk IO; md (RAID) resync/check implicated

On Fri, 2010-06-25 at 11:50 +0100, Ian Jackson wrote:
> Ben Hutchings writes ("Re: Bug#584881: Lockups under heavy disk IO; md (RAID) resync/check implicated"):
> > I/O barriers are block I/O operations (not specific to md) that inhibit
> > reordering of read and write operations.  They certainly should not be
> > blocking operations.  Also, device-mapper did not support barriers until
> > after 2.6.26 so md will not be using them in the configuration you are
> > using.
> No, I think there are two meanings of the word "barrier".  AFAICT md
> has its own thing which it confusingly calls a "barrier"; it can be
> "raised" and "lowered".

Oh, great!  I wondered whether this was the case but I could only find
discussion of md vs I/O barriers.  Do you have any reference for
documentation of md barriers?


Ben Hutchings
Once a job is fouled up, anything done to improve it makes it worse.

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