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