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    SubjectRe: weird throughput on write to SATA disk
    On Mon, 13 Oct 2008 14:07:15 -0700
    "Grant Grundler" <grundler@google.com> wrote:

    > On Mon, Oct 13, 2008 at 12:19 PM, kenneth johansson <ken@kenjo.org> wrote:
    > > When writing data to /dev/sdb (that is the whole disk and no filesystem)
    > > it starts out ok around 100MB/sec but soon end up doing considerably
    > > worse. For prolonged times lasting several minutes it hovers in the
    > > 20-30MB/sec.
    >
    > Is the application using "O_DIRECT"?
    > If not, could be issue with how VM writeback is (not) working.

    Or just mashing up the I/O horribly. Would also be worth turning the CFQ
    scheduler off or applying Arjan van de Ven's patches to fix the ioprio of
    the kernel writeout threads. That last patch makes a huge difference here.

    Alan


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