Flow-control may well just mask the real problem. Did your throughput improve? Also, does that mean flow-control is on for all ports on the switch...? IIUC, then such "global pause" flow-control will mean switchports with links to upstream network devices will also be paused if the switch is attempting to pass packets from those ports down to a congested host.
Are your ring buffers tuned up as high as possible, `ethtool -g <ifname>`?
On 11 September 2017 at 23:09, Andreas Herrmann <andreas@xxxxxxxx> wrote:
Hi,
flow control was active on the NIC but not on the switch.
Enabling flowcontrol for both direction solved the problem:
flowcontrol receive on
flowcontrol send on
Port Send FlowControl Receive FlowControl RxPause TxPause
admin oper admin oper
---------- -------- -------- -------- -------- ------------- -------------
Et17/1 on on on on 0 64500
Et17/2 on on on on 0 33746
Et17/3 on on on on 0 17126
Et18/1 on on on on 0 36948
Et18/2 on on on on 0 39628
Regards,
Andreas
On 08.09.2017 13:57, Andreas Herrmann wrote:
> Hello,
>
> I have a fresh Proxmox installation on 5 servers (Supermciro X10SRW-F, Xeon
> E5-1660 v4, 128 GB RAM) with each 8 Samsung SSD SM863 960GB connected to a
> LSI-9300-8i (SAS3008) controller used as OSDs for Ceph (12.1.2)
>
> The servers are connected to two Arista DCS-7060CX-32S switches. I'm using
> MLAG bond (bondmode LACP, xmit_hash_policy layer3+4, MTU 9000):
> * backend network for Ceph: cluster network & public network
> Mellanox ConnectX-4 Lx dual-port 25 GBit/s
> * frontend network: Intel Corporation 82599ES 10-Gigabit SFI/SFP+ dual-port
>
> Ceph is quite a default installation with size=3.
>
> My problem:
> I'm issuing a dd (dd if=/dev/urandom of=urandom.0 bs=10M count=1024) in a test
> virtual machine (the only one running in the cluster) with arround 210 MB/s. I
> get output drops on all switchports. The drop rate is between 0.1 - 0.9 %. The
> drop rate of 0.9 % is reached when writing with about 1300MB/s into ceph.
>
> First I thought about a problem with the Mellanox cards and used the Intel
> cards for ceph traffic. The problem also exists.
>
> I tried quite a lot and nothing help:
> * changed the MTU from 9000 to 1500
> * changed bond_xmit_hash_policy from layer3+4 to layer2+3
> * deactivated the bond and just used a single link
> * disabled offloading
> * disabled power management in BIOS
> * perf-bias 0
>
> I analyzed the traffic via tcpdump and got some of those "errors":
> * TCP Previous segment not captured
> * TCP Out-of-Order
> * TCP Retransmission
> * TCP Fast Retransmission
> * TCP Dup ACK
> * TCP ACKed unseen segment
> * TCP Window Update
>
> Is that behaviour normal for ceph or has anyone ideas how to solve that
> problem with the output drops at switch-side
>
> With iperf I can reach full 50 GBit/s on the bond with zero output drops.
>
> Andreas
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~Blairo
~Blairo
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