[Gluster-users] help, glusterfs test caused very high tcp segment retransmission rate (Collin Douglas)

[Dai, Manhong]

Hi Collin,

  Thanks a lot for your help. The interconnect is Gigabit Ethernet.

  I am guessing that it is caused by the router. Computing nodes that connect to this router always retransmit 5% of segments under heavy load. My test on other router has lower ratio, around 0.3%. I am about to replace the router and perform another test.

  Anyway this problem is not related to glusterfs at all. Although I do have another question that is about glusterfs, which I will send in a separated email.

Best,
Manhong

Date: Mon, 25 Aug 2008 08:41:25 -0500
From: Collin Douglas <cbd at adfitech.com>
Subject: Re: [Gluster-users] help, glusterfs test caused very high tcp
	segment retransmission rate
Cc: gluster-users at gluster.org
Message-ID: <48B2B685.2050603 at adfitech.com>
Content-Type: text/plain; charset="ISO-8859-1"

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This sounds a lot like a physical layer issue -- most notably a 
speed/duplex issue.  Any time I've seen a large number of retransmits 
occur during heavy load, this is what I suspect.

That said, I don't know what type of interconnect you're using.  Tell us 
more about your configuration.

- -Collin

Dai, Manhong wrote:
>
>
> Hi,
>
>  
>    I found the aggregated IO speed is only about 100MB/s on 4 Giga-bit 
> Brick. This test is done over 12 computing nodes with command dd 
> if=/dev/zero of=bar bs=1048576 count=20480. Because our brick has very 
> fast local IO speed, the problem could be network.
>
>
>   Then I found computing nodes got too many retransmited segments 
> during test according to netstat -st. The retransmission ratio is 
> about 5%, but brick node has a normally low transmission rate.
>
>
>   Could some shed some light?
>
> Best,
> Manhong
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