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    SubjectRe: Abysmal disk performance, how to debug?
    Date
    20 Oca 2007 Cts 20:03 tarihinde şunları yazmıştınız:
    > On Sat, Jan 20, 2007 at 07:52:53PM +0200, Ismail Dönmez wrote:
    > > 20 Oca 2007 Cts 19:45 tarihinde ??unlar?? yazm????t??n??z:
    > > [...]
    > >
    > > > > vaio cartman # hdparm -tT /dev/hda
    > > > >
    > > > > /dev/hda:
    > > > > Timing cached reads: 1576 MB in 2.00 seconds = 788.18 MB/sec
    > > > > Timing buffered disk reads: 74 MB in 3.01 seconds = 24.55 MB/sec
    > > > >
    > > > >
    > > > > [~]> time dd if=/dev/zero of=/tmp/1GB bs=1M count=1024
    > > > > 1024+0 records in
    > > > > 1024+0 records out
    > > > > 1073741824 bytes (1,1 GB) copied, 77,2809 s, 13,9 MB/s
    > > > >
    > > > > real 1m17.482s
    > > > > user 0m0.003s
    > > > > sys 0m2.350s
    > > >
    > > > That's not bad at all ! I suspect that if your system becomes
    > > > unresponsive, it's because real writes start when the cache is full.
    > > > And if you fill 512 MB of RAM with data that you then need to flush on
    > > > disk at 14 MB/s, it can take about 40 seconds during which it might be
    > > > difficult to do anything.
    > > >
    > > > Try lowering the cache flush starting point to about 10 MB if you want
    > > > (2% of 512 MB) :
    > > >
    > > > # echo 2 >/proc/sys/vm/dirty_ratio
    > > > # echo 2 >/proc/sys/vm/dirty_background_ratio
    > >
    > > After that I get,
    > >
    > > [~]> time dd if=/dev/zero of=/tmp/1GB bs=1M count=1024
    > > 1024+0 records in
    > > 1024+0 records out
    > > 1073741824 bytes (1,1 GB) copied, 41,7005 s, 25,7 MB/s
    > >
    > > real 0m41.926s
    > > user 0m0.007s
    > > sys 0m2.500s
    > >
    > >
    > > not bad! thanks :)
    >
    > It is not expected to increase write performance, but it should help
    > you do something else during that time, or also give more responsiveness
    > to Ctrl-C. It is possible that you have fast and slow RAM, or that your
    > video card uses shared memory which slows down some parts of memory
    > which are not used anymore with those parameters.

    Thanks I will try to upgrade RAM but for now at least responsiveness seems to
    be better.

    Regards,
    ismail
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