Re: weird throughput on write to SATA disk

[kenneth johansson]

On Mon, 2008-10-13 at 14:07 -0700, Grant Grundler wrote:
> On Mon, Oct 13, 2008 at 12:19 PM, kenneth johansson <ken@xxxxxxxxx> 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"?

no just open then write no fancy stuff

> If not, could be issue with how VM writeback is (not) working.

the access pattern is the simplest possible. Is there any knobs I could
try to adjust.

> Can you reproduce this using fio or even "dd"?
> (See git://git.kernel.dk/fio)

dd is having the same effect. 


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