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    SubjectRe: io performance...
    I was going to say, doesn't the kernel set the FUA bit on the write 
    request to push important flushes through the disk's write-back cache?
    Like for filesystem journal flushes?


    Alan Cox wrote:
    > Not always. If you have a cache flush command and the OS knows about
    > using it, or if you don't care if the data gets lost over a power
    > failure (eg /tmp and swap) it makes sense to force it.
    >
    > The raid controller drivers that fake scsi don't always fake enough of
    > scsi to report that they support cache flushes and the like. That
    > doesn't mean the controller itself is neccessarily doing one thing or
    > the other.
    >
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