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    SubjectRe: Abysmal disk performance, how to debug?
    On Sat, Jan 20, 2007 at 10:16:15PM +0200, Ismail Dönmez wrote:
    > 20 Oca 2007 Cts 22:10 tarihinde, Tim Schmielau ??unlar?? yazm????t??:
    > [...]
    > >
    > > 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

    No, your measure is wrong because time measures "dd" and sync is done
    after. Either use Tim's method (time sync) or the one I proposed in
    previous mail (time dd | sync). Anyway, in your situation with a very
    small buffer, this should not change by more than half a second or so.

    Willy

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