Mellanox SB7800 and LinkX 200GbE cables (200Gb/s to 2x100Gb/s)

Infrastructure & Networking Switches and Gateways InfiniBand/VPI Switch Systems
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RHEL 8.4
MLNX_OFED_LINUX-5.7-1.0.2.0-rhel8.4

lspci | grep Mellanox
a1:00.0 Infiniband controller: Mellanox Technologies MT28908 Family [ConnectX-6]

Cable part number:
MCP7H50-H002R26

ibstatus
Infiniband device ‘mlx5_0’ port 1 status:
default gid: fe80:0000:0000:0000:e8eb:d303:00ef:5d22
base lid: 0xe
sm lid: 0x1
state: 4: ACTIVE
phys state: 5: LinkUp
rate: 25 Gb/sec (1X EDR)
link_layer: InfiniBand

mlxlink -d mlx5_0

Operational Info
…
State : Active
Physical state : LinkUp
Speed : IB-EDR
Width : 1x
FEC : Standard LL RS-FEC - RS(271,257)
Loopback Mode : No Loopback
Auto Negotiation : ON

Supported Info
…
Enabled Link Speed : 0x00000075 (HDR,EDR,FDR,QDR,SDR)
Supported Cable Speed : 0x0000007f (HDR,EDR,FDR,FDR10,QDR,DDR,SDR)

Troubleshooting Info
…
Status Opcode : 0
Group Opcode : N/A
Recommendation : No issue was observed.

Tool Information
…
Firmware Version : 20.32.2004
amBER Version : 2.02
MFT Version : mft 4.21.0-99

How to set the speed to 100GbE with these cables? Currently they run only in 25GbE (1XEDR).

mlxlink -d mlx5_0 -p 1 --speeds edr
mlxlink -d mlx5_0 -p 1 --speeds hdr

Both gives the same results 25GbE (1xEDR)

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Apparently the Mellanox SB7800 can only handle 25Gb/s lanes so 2 x 50Gb for split cables doesn’t work because of this.

1 Like
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EDR switch not support split cable, you can only get 1x, 4x link.
HDR can get 1x,2x,4x link

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