Messages in this thread | | | Date | Mon, 13 Oct 2008 23:39:33 +0100 | From | Alan Cox <> | Subject | Re: weird throughput on write to SATA disk |
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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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