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    SubjectRe: weird throughput on write to SATA disk
    On Mon, Oct 13, 2008 at 12:19 PM, kenneth johansson <> 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.

    Can you reproduce this using fio or even "dd"?
    (See git://


    > This happens on two different SATA disk one samsung and one seagate and
    > on both 2.6.26 and 2.6.27 kernel. The disk are connected to the external
    > esata connector. Controller is 00:1f.2 SATA controller: Intel
    > Corporation 82801HB (ICH8) 4 port SATA AHCI Controller (rev 02)
    > What could be the reason for this ?? reading is no problem.

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