[ewg] 200m cable results in slower rdma read performance? [ CC Anti-Virus checked ]

[koen_segers at computacenter.com]

Hi, 

 

In my test setup I have 3 servers of which 2 are residing in Datacenter1
and the other in Datacenter2.

If I do a rdma test between datacenters, I get a much lower performance
than if I would do the test between servers residing in the same
datacenter.

 

 

DC1: gpfsprod1n1, gpfsprod1n3

DC2: gpfsprod1n2

 

08:54:48|root at gpfsprod1n1:~ 0 # qperf -t 5  cic-gpfsprod1n2
rc_rdma_write_bw

rc_rdma_write_bw:

    bw  =  1.9 GB/sec

08:54:59|root at gpfsprod1n1:~ 0 # qperf -t 5  cic-gpfsprod1n3
rc_rdma_write_bw

rc_rdma_write_bw:

    bw  =  3.39 GB/sec

 

 

The setup contains two pairs of edge switches (on each datacenter one
pair) and two spine switches (each datacenter one), configured as a non
blocking fat tree.

So:

The servers are connected to the edge switches.

The spine switches are connected to all edge switches.

 

These are the cables we are using:

.         Length 5m Vendor Name: WLGORE Code: QSFP+ Vendor PN:
498385-B24 Vendor Rev: D Vendor SN xxxx

.         Length 200m Vendor Name: MOLEX Code: QSFP+ Vendor PN:
106410-1200 Vendor Rev: A Vendor SN xxxx

 

 

Can someone tell me why this is so? And maybe how I can solve this?

 

Best regards,

 

 

Koen Segers

Enterprise Consultant

 

Computacenter

Services & Solutions

 

Ikaroslaan 31

B-1930 Zaventem

Belgium

 

Tel: +32 2 704 94 67

Fax: +32 2 704 95 95

Mob: +32 497 909353

koen_segers at computacenter.com <mailto:koen_segers at computacenter.com> 

www.computacenter.com/benelux <http://www.computacenter.com/benelux> 

 



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