inconsistent HTTP download speeds on a LAN - Networking

This is a discussion on inconsistent HTTP download speeds on a LAN - Networking ; Hello, We have an Apache 2.0.52 server on RHEL ES4u4 (2.6.9-42.ELsmp) that is running a CGI application. As part of the application, attachments can be downloaded by users. The server is connect via GigE to a central switch, and various ...

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Thread: inconsistent HTTP download speeds on a LAN

  1. inconsistent HTTP download speeds on a LAN

    Hello,

    We have an Apache 2.0.52 server on RHEL ES4u4 (2.6.9-42.ELsmp) that is running
    a CGI application. As part of the application, attachments can be downloaded by
    users. The server is connect via GigE to a central switch, and various clients
    are connected via LAN to various switches, which then connect to the central
    switch.

    For some clients the attachments are downloaded at 50-100 KB/s, but for others
    they get 2+ MB/s. The slow clients are of different OSes (Linux, OS X, and
    Windows) and are all on different VLANs. The fast clients are also various
    OSes and VLANs (i.e., switches / routers don't seem to be a common element).

    I'm trying to figure what the fast clients have in common, and how they are
    different from the slow ones.

    I've done a few tcpdumps, and the only difference between fast and slow systems
    (using the same OS) is that TCP window size gets to 60 KB in ~0.02s for the
    fast clients, but takes up to 0.80-1.14 seconds for the slow ones. I'm thinking
    this has something to do with TCP ramp up algorithms, but can't seem to figure
    out the differences between the two.

    One of the slow machines is Fedora 8:

    Linux lnx-slowA 2.6.24.3-50.fc8 #1 SMP Thu Mar 20 13:39:08 EDT 2008
    x86_64 x86_64 x86_64 GNU/Linux

    Another is Fedora 6:

    Linux lnx-slowB 2.6.18-1.2798.fc6 #1 SMP Mon Oct 16 14:54:20 EDT 2006
    i686 i686 i386 GNU/Linux

    One of the fast machines is Fedora 7:

    Linux lnx-fast 2.6.23.15-80.fc7 #1 SMP Sun Feb 10 17:29:10 EST 2008
    i686 i686 i386 GNU/Linux

    Any ideas?

    Thanks for any info.

    --
    David Magda
    Because the innovator has for enemies all those who have done well under
    the old conditions, and lukewarm defenders in those who may do well
    under the new. -- Niccolo Machiavelli, _The Prince_, Chapter VI

  2. Re: inconsistent HTTP download speeds on a LAN

    Seems like the easiest thing to eliminate network hardware would be to
    pull a slow machine and move it the the location of a fast one, using
    the fast ones connection - right down to the cable. That would
    positively eliminate everything but the machine itself. From there you'd
    have to look at similarities between the slow computers.

    Kurt

    David Magda wrote:
    > Hello,
    >
    > We have an Apache 2.0.52 server on RHEL ES4u4 (2.6.9-42.ELsmp) that is running
    > a CGI application. As part of the application, attachments can be downloaded by
    > users. The server is connect via GigE to a central switch, and various clients
    > are connected via LAN to various switches, which then connect to the central
    > switch.
    >
    > For some clients the attachments are downloaded at 50-100 KB/s, but for others
    > they get 2+ MB/s. The slow clients are of different OSes (Linux, OS X, and
    > Windows) and are all on different VLANs. The fast clients are also various
    > OSes and VLANs (i.e., switches / routers don't seem to be a common element).
    >
    > I'm trying to figure what the fast clients have in common, and how they are
    > different from the slow ones.
    >
    > I've done a few tcpdumps, and the only difference between fast and slow systems
    > (using the same OS) is that TCP window size gets to 60 KB in ~0.02s for the
    > fast clients, but takes up to 0.80-1.14 seconds for the slow ones. I'm thinking
    > this has something to do with TCP ramp up algorithms, but can't seem to figure
    > out the differences between the two.
    >
    > One of the slow machines is Fedora 8:
    >
    > Linux lnx-slowA 2.6.24.3-50.fc8 #1 SMP Thu Mar 20 13:39:08 EDT 2008
    > x86_64 x86_64 x86_64 GNU/Linux
    >
    > Another is Fedora 6:
    >
    > Linux lnx-slowB 2.6.18-1.2798.fc6 #1 SMP Mon Oct 16 14:54:20 EDT 2006
    > i686 i686 i386 GNU/Linux
    >
    > One of the fast machines is Fedora 7:
    >
    > Linux lnx-fast 2.6.23.15-80.fc7 #1 SMP Sun Feb 10 17:29:10 EST 2008
    > i686 i686 i386 GNU/Linux
    >
    > Any ideas?
    >
    > Thanks for any info.
    >


  3. Re: inconsistent HTTP download speeds on a LAN

    David Magda wrote:
    > Hello,
    >
    > We have an Apache 2.0.52 server on RHEL ES4u4 (2.6.9-42.ELsmp) that is running
    > a CGI application. As part of the application, attachments can be downloaded by
    > users. The server is connect via GigE to a central switch, and various clients
    > are connected via LAN to various switches, which then connect to the central
    > switch.
    >
    > For some clients the attachments are downloaded at 50-100 KB/s, but for others
    > they get 2+ MB/s. The slow clients are of different OSes (Linux, OS X, and
    > Windows) and are all on different VLANs. The fast clients are also various
    > OSes and VLANs (i.e., switches / routers don't seem to be a common element).
    >


    Stupid trivial question, but are all the clients using correct duplex?

  4. Re: inconsistent HTTP download speeds on a LAN

    On 2008-04-24, Jurgen Haan wrote:
    > Stupid trivial question, but are all the clients using correct duplex?


    Not the case here.

    Something that I forgot to mention in my original post: the "slow" clients
    are not acutally slow everywhere, just with that particular web server. They
    can download at relatively high speeds (2+ MB/s) from a different web server,
    that's also running Apache and Red Hat (though different versions).

    The TCP settingss (as shown via 'sysctl -a | grep tcp') are the same between
    the two servers.

    It's just with this particular web server that some workstations are fast and
    some are slow.



  5. Re: inconsistent HTTP download speeds on a LAN

    On 2008-04-23, Kurt wrote:
    > Seems like the easiest thing to eliminate network hardware would be to
    > pull a slow machine and move it the the location of a fast one, using
    > the fast ones connection - right down to the cable. That would
    > positively eliminate everything but the machine itself. From there you'd
    > have to look at similarities between the slow computers.


    Still slow.

    One thing that I forgot to mention: the "slow" clients are only slow for
    this particular web server. If I try to download a file from another internal
    web server the speed is fine.

    It's just with this particular one some clients are fast and some are slow.
    The TCP settings ('sysctl -a | grep tcp') are the same between the two
    servers, though there are slight differences between the two web servers: one
    has httpd-2.0.52-22.ent, while the other has httpd-2.0.52-25.ent. One is
    RHEL ES 4u4 (2.6.9-42.ELsmp), while the other is RHEL AS 4u2 (2.6.9-22.ELsmp).



  6. Re: inconsistent HTTP download speeds on a LAN

    On 2008-04-24, David Magda wrote:
    > Something that I forgot to mention in my original post: the "slow" clients
    > are not acutally slow everywhere, just with that particular web server. They
    > can download at relatively high speeds (2+ MB/s) from a different web server,
    > that's also running Apache and Red Hat (though different versions).
    >
    > The TCP settingss (as shown via 'sysctl -a | grep tcp') are the same between
    > the two servers.
    >
    > It's just with this particular web server that some workstations are fast and
    > some are slow.


    Just a quick update on the two web servers: going through 'sysctl -a' output
    for both machines and doing a diff(1), there are no notable differences
    between the two besides things like hostname and kernel versions. The only
    differences under net.* is that one machine has an extra interface plumbed.



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