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    SubjectRe: Interesting disk throughput performance problem
    On Sun, Jul 22, 2001 at 01:20:24PM +0400, Hans Reiser wrote:
    >
    > I'm just guessing here, but is write caching active on one but not the other?

    What do you mean?
    That he should activate the write caching in all his drives?
    I thought that was plain stupid and wrong, because the filesystem
    expects journal data to hit the disk immedialtely. The journal
    is written synchronously, isn't it?
    So I would expect you to advise everybody to deactivate any
    caching in drives and controllers. An the we are back with
    Jimmie's question: the throughput performance of his drives
    is bad, and the (theoretically) fastest drive is worst.

    Regards,
    Toon (running a newsserver with reiserfs-3.5.32 on top of LVM-0.9.1-beta7 on
    top of DAC960 hardware RAID5 with write-caching turned off, using linux-2.2.19)

    > Jimmie Mayfield wrote:
    > >
    > > Hi. I'm running into some disk throughput issues that I can't explain.
    > > Hopefully someone reading this can offer an explanation.
    > >
    > > One of my machines is running 2.4.5 and has 2 hard drives: a 7200 rpm
    > > ATA100 Maxtor and a 5400 rpm ATA33 IBM. Each drive is a master on its own
    > > controller (AMI CMD649 as found on the IWill KT266-R). Both drives contain
    > > reiserfs 3.6x filesystems.
    > >
    > > By all local benchmarks, the 7200 rpm drive is the faster drive. But this
    > > doesn't seem to be the case for large files originating from remote clients.
    > > Witness:
    > >
    > > My crude test involves scp'ing a 100MB file from another machine on my home
    > > network over 100bT ethernet.
    > >
    > > 1) scp to the 5400rpm drive: roughly 10MB/sec.
    > > 2) scp to the 7200rpm drive: roughly 2MB/sec.
    > >
    > > I've tried 'tail' and 'notail' mount options with no change (as expected since
    > > this is a single large file). I suspect that the machine would become CPU-bound
    > > somewhere in the 20MB/sec range (see below for my reasoning).
    > >
    > > I see the same sort of behavior using Samba though not nearly as
    > > pronounced (the 5400rpm drive is merely 2x as fast as the 7200rpm drive).
    > >
    > > Okay. Since the test involved 2 separate drives with different geometries,
    > > I figured this might be due to physical block location. Perhaps the file
    > > is getting allocated to the fastest cylinders on the 5400 rpm drive and
    > > the slowest cylinders on the 7200 rpm drive. Or it could be a fragmentation
    > > issue.
    > >
    > > So I tried the test locally: with the file stored on the 5400rpm drive,
    > > scp it to localhost and write it to the 7200rpm drive. Results were a little
    > > below 10MB/sec (CPU near 100% presumably due to encrypting/decrypting on
    > > the fly).
    > >
    > > Any ideas why the 7200rpm drive performs so poorly for remote clients but
    > > performs wonderfully well when those same operations are performed locally?
    > >
    > > Jimmie
    > >
    > > -
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