[lustre-discuss] lustre causing dropped packets

[Brian Andrus]

Shawn,

Flow control is configured and these connections are all on the same 40g 
subnet and all directly connected to the same switch.

I'm a little new with using lnet_selftest, but as I run it 1:1, I do see 
the dropped packets go up on the client node pretty significantly when I 
run it. The node I set for server does not drop any packets.

Brian Andrus


On 12/5/2017 9:20 AM, Shawn Hall wrote:
> 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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