Re: High TCP retransmission rates, only with Ceph

Paweł Sadowsk <ceph@xxxxxxxxx> · Mon, 16 Apr 2018 09:12:08 +0200



    Those retransmission happen at the TCP handshake or after that?
      Did you checked error counters on your NICs? Maybe your radosgw is
      sending too much requests to OSDs.

    
    On 04/15/2018 10:54 PM, Robert Stanford
      wrote:

    
         I should have been more clear.  The TCP retransmissions are on
        the OSD host.

      
        On Sun, Apr 15, 2018 at 1:48 PM, Paweł
          Sadowski <ceph@xxxxxxxxx>
          wrote:

          On 04/15/2018 08:18 PM, Robert Stanford wrote:

              
                 Iperf gives about 7Gb/s between a radosgw host and one
                of my OSD hosts (8 disks, 8 OSD daemons, one of 3 OSD
                hosts).  When I benchmark radosgw with cosbench I see
                high TCP retransmission rates (from sar -n ETCP 1).  I
                don't see this with iperf.  Why would Ceph, but not
                iperf, cause high TCP retransmission rates?

              
            Most probably your application (radosgw in this case) is not
            able to process requests fast enough and some packets are
            dropped.

                
                -- 

                PS

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