[lustre-discuss] lustre causing dropped packets

[Shawn Hall]

Hi Brian,

Do you have flow control configured on all ports that are on the network path?  Lustre has a tendency to cause packet losses in ways that performance testing tools don’t because of the N to 1 packet flows, so flow control is often necessary.  Lnet_selftest should replicate this behavior.

Is there a point in the network path where the link bandwidth changes (e.g. 40 GbE down to 10 GbE, or 2x40 GbE down to 1x40 GbE)?  That will commonly be the biggest point of loss if flow control isn’t doing its job.

Shawn

On 12/5/17, 11:49 AM, "lustre-discuss on behalf of jongwoohan at naver.com" <lustre-discuss-bounces at lists.lustre.org on behalf of jongwoohan at naver.com> wrote:

    Did you check your connection with iperf and iperf3 in TCP bandwidth? in that case, these tools cannot find out packet drops.
    
    Try checking out your block device backend responsibility with benchmark tools like vdbench or bonnie++. Sometimes bad block device causes incorrect data transfer.
    
    -----Original Message-----
    From: "Brian Andrus"<toomuchit at gmail.com> 
    To: "lustre-discuss at lists.lustre.org"<lustre-discuss at lists.lustre.org>; 
    Cc: 
    Sent: 2017-12-06 (수) 01:38:04
    Subject: [lustre-discuss] lustre causing dropped packets
     
    All,
    
    I have a small setup I am testing (1 MGS, 2 OSS) that is connected via 
    40G ethernet.
    
    I notice that when I run anything that writes to the lustre filesystem 
    causes dropped packets. Reads do not seem to cause this. I have also 
    tested the network (iperf, iperf3, general traffic) with no dropped packets.
    
    Is there something with writes that can cause dropped packets?
    
    
    Brian Andrus
    
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