On Mon, Oct 13, 2008 at 2:22 PM, kenneth johansson <ken@xxxxxxxxx> 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@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. 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-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
