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    SubjectRe: Abysmal disk performance, how to debug?
    On Sat, 20 Jan 2007, Ismail Dönmez wrote:

    > 20 Oca 2007 Cts 22:10 tarihinde, Tim Schmielau şunları yazmıştı:
    > >
    > > Note that these dd "benchmarks" are completely bogus, because the data=20
    > > doesn't actually get written to disk in that time. For some enlightening=20
    > > data, try
    > >
    > > time dd if=3D/dev/zero of=3D/tmp/1GB bs=3D1M count=3D1024; time sync
    ^^^^
    > >
    > > The dd returns as soon as all data could be buffered in RAM. Only sync=20
    > > will show how long it takes to actually write out the data to disk.
    > > also explains why you see better results is writeout starts earlier.
    >
    > Still not that bad:
    >
    > [~]> time dd if=/dev/zero of=/tmp/1GB bs=1M count=1024;sync
    > 1024+0 records in
    > 1024+0 records out
    > 1073741824 bytes (1,1 GB) copied, 53,3194 s, 20,1 MB/s
    >
    > real 0m53.517s
    > user 0m0.003s
    > sys 0m3.193s
    >

    That's not the point, you still measured the same as before (but you might
    have noticed that, after printing the results, the shell prompt took some
    time to appear). I appended "time sync" to the command to show that
    (depending on the amount of available memory) actually most of the time
    is spent in the "sync", not the "dd".

    Tim
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