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    SubjectRe: SATA RAID5 speed drop of 100 MB/s
    Jeff Garzik wrote:
    > Carlo Wood wrote:
    >> The dmesg output of 33480a0ede8dcc7e6483054279008f972bd56fd3 (thus
    >> "before") is:
    > [...]
    >> And the dmesg output of 551c012d7eea3dc5ec063c7ff9c718d39e77634f (thus
    >> "after") is:
    > [...]
    > Your disk configurations are quite radically different between the two
    > kernels (see attached diff for key highlights).
    > The new behavior of the more recent kernel (551c012d7...) is that it now
    > fully drives your hardware :) The reset problems go away, NCQ is
    > enabled, and if you had 3.0Gbps drives (you don't) they would be driven
    > at a faster speed.
    > Given that some drives might be better tuned for benchmarks in
    > non-queued mode, and that a major behavior difference is that your
    > drives are now NCQ-enabled, the first thing I would suggest you try is
    > disabling NCQ:
    > Other indicators are the other changes in the "ahci 0000:00:1f.2:
    > flags:" line, which do affect other behaviors, though none so important
    > to RAID5 performance as NCQ, I would think.
    > Turning on NCQ also potentially affects barrier behavior in RAID, though
    > I'm guessing that is not a factor here.

    Ah.. right. That should have enabled NCQ. Me slow today. :-)

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