IBM POWER8 Networking via Direct Attach Cables

I recently had a project where my company sold POWER8 servers to the customer along with some Lenovo servers and Lenovo G8272 network switches. The switches have 48x 1/10 Gb ports + 6x 40 Gb ports.

To save on cost, it's possible to use Direct Attach Cables (DACs) to connect servers to the switches without buying SFPs nor FC cables. List price comparison:

• Lenovo 10GBASE-SR SFP+ Transceiver (46C3447) = $629
• Lenovo 5m LC-LC OM3 MMF Cable (00MN508) = $58
• To connect 1 server (4 ports) to switches (4 ports) = 8x $629 + 4x $58 = $5,264.

In contrast, with DACs, you only need 1 cable which includes the SFPs (copper):

• Lenovo 5m Passive SFP+ DAC Cable (90Y9433) = $210
• Lenovo 5m Active DAC SFP+ Cable (00VX117) =  $290
• Active are often used for switch-to-switch connectivity.
• To connect 1 server (4 ports) to switches (4 ports) = 4x  $210 = $840.

 DACs are 16% the cost! Or 6.3 times cheaper. These prices are based on publicly available list prices. They might be different depending on your region and distributor.

The POWER8 servers (S822) have the following Ethernet adapter: EN0U -- PCIe2 4-Port (10Gb+1GBE) Copper SFP+RJ45 Adapters. According to the redbook (guide), these adapters require Active Copper DACs.

I actually used the Passive DACs that I used for the Lenovo servers, and the cables worked just fine. The AIX team configured 2 Virtual Input/Output Servers (VIOS) on each POWER8 system, and each POWER8 system had 4 of these adapters. We also configured LACP for each VIOS, so the total bandwidth available to each VIOS was 40 Gb.

So even though the redbook says that Active DACs are required, the passive ones work just fine. Also the redbook only lists 1 meter, 3 meter & 5 meter cables (since they're active) and no mention of passive cables.