I was told that the reason I'm having network performance issues is due to "generic receive offload" on eth0. I was told to use the following command:

Does anyone know what exactly this is disabling / correcting for my NIC performance?

Turning it off will prevent the nic from buffering inbound data before sending to the cpu ... what sort of performance issues were you having ? .. latency ?

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Yes I had latency but only on the virtual guest systems, not the host OS. When I build my host OS (Linux) on the server, everything was super fast. Then I installed VirtualBox software and started building guest systems. When I transfered a 1GB file to the host from my PC, it transfered a 1GB file in about 30 seconds. When I transfered the same file from my PC to the guest systems, it would take about 4-5 hours. The latency was worse the more CPU's I assigned to the guest systems.

Is this bad to turn off? I can't see how this would function with the 'gro' option enabled.

I assume you mean pc to pc is OK where pc to VM is bad.

If you have issues between VM and host file transfer then I'd think it would be the hard drive causing it.

Also how have you set the nic? bridged or local?

All I can say is give it a try .. there are a lot of layers in the process that could be affecting transfer performance

I can tell you that when I transfer a 1 GB file from PC to VM with GRO enabled = 4 hours. When I transfer from PC to VM with GRO disabled = 2 minutes.

I can tell you for sure it's NOT the hard drive or anything else based on simply turning that off. I have the NIC bridged in VirtualBox.

How do you configure GRO to stay off when your host reboots? Is this something that I can add to the interface config file, e.g.: /etc/sysconfig/network-scripts/ifcfg-eth1. If so, what would the entry look like? Thanks!