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Thread: [SOLVED] Really slow imap performance on zcs 5.0.9

  1. #1
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    Default [SOLVED] Really slow imap performance on zcs 5.0.9

    Hi,
    i did set up a new Zimbra Open source Edition 5.0.9 in a Xen domu (Ubuntu 8.04 LTS 62bit). Almost everything worked fine, User migration, syncing mails ....
    Server is pretty a fresh install but i have unbelievable performance problems with the imap server but only with imap Connections. Everthing else looks pretty normal.

    Server is a Dual core(3 Ghz) with 4 GB ram
    zimbra domu uses one CPU and 768 Mb Ram.
    Zimbra serves only Mailaccounts for 4-5 Users so it should not require much cpu or ram.

    But whatever i tried i can only download messages from the zimbra-imap server with an average of 15-20 Kb/s what is really sucking cause we have a lot of huge mails.
    Tested with Apple Mailclient, Thunderbird (Linux/win) and everything from to different Networks. Even Zimbra desktop is not fast with this.



    Antivirus and Spamscanner are not running on the zimbra Server. I checked it twice that it is not running. AV/AS is running on our mx server, cause i using a fine tuned setup with exim rules.

    Except of missing AV/AS the zimbra configuration is a standard install with zcs community build for ubuntu.

    On my old mailserver (celeron 2.4 Ghz 512 MB Ram) i used courier and i get an average up to 600 Kb/s but the old server was additionally running exim/AV/AS/LAMP-stack and it was still 20 times faster than the new one.

    I tested copying some data with scp to the zimbra server (maybe something broken with the Connection) but the speed looks usall.
    I checked if maybe the dom0 or the other domu`s are consuming IO/CPU but they are running idle. After this i disabled mail indexer for some accounts but it did not changed anything.

    i use cacti to graph my servers and the zimbra server has always a load between 0.5-1, even nobody is fetching mails. Is this normal?

    I took a look into /opt/zimbra/zmstat/mailboxd.csv but if i dont know what im looking for it is not helpfull.

    Can anybody give me some tips where i should look, to locate the problem? Or does zimbra just certain amount of Ram before it will work like it should. Would be 1 GB solve the Problem?

  2. #2
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    Hi,
    i increased the amount of Ram to 1200 Mb but still no better performance.
    Anybody an idea ?

  3. #3
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    Hi,
    i solved this problem myself. It was a XEN/Network related issue. After disabling TCP Checksumming everything worked fine.

  4. #4
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    How did you disable TCP Checksumming ? We are having slow IMAP issues as well. Thanks

  5. #5
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    Hi,
    insert this line after your iface config in /etc/network/interfaces:

    post-up ethtool -K eth0 tx off

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