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Message-ID: <da824cf30810131434r34179666kc8d075c7eecdbbae@mail.gmail.com> Date: Mon, 13 Oct 2008 14:34:00 -0700 From: "Grant Grundler" <grundler@...gle.com> To: "kenneth johansson" <ken@...jo.org> Cc: linux-ide@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: weird throughput on write to SATA disk On Mon, Oct 13, 2008 at 2:22 PM, kenneth johansson <ken@...jo.org> wrote: > On Mon, 2008-10-13 at 14:07 -0700, Grant Grundler wrote: >> On Mon, Oct 13, 2008 at 12:19 PM, kenneth johansson <ken@...jo.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"? > > 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. Can you try "dd oflag=direct if=/dev/null of=/dev/sdb bs=64k"? Or try with "sgp_dd"? It's part of sg3-utils package. thanks, grant -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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