Showing results for 
Search instead for 
Did you mean: 

VM-FEX and VMDirectPath I/O with vMotion



Just would like to have your thoughts about this solution. From what I've heard it is already possible to do it with vSphere 5...yet I have not seen a lot of information from VMware side...nor a lot of enthusiasm either in Cisco site. I think that over Power Point the solution looks very cool (outstanding performance improvement of both runtime application and networking throughput), but at the same time I'm not seeing a lot of info, case studies, etc. about this.

Does anybody know of any customer already implementing the solution? Does it work ok? Is it advisable to position it to everybody, or rather to just a very specific group of customers??

Thanks a lot,


Manish Tandon
Cisco Employee
Cisco Employee


Yes, DirectPath I/O with vMotion using VM-FEX is possible in vSphere 5.0 and is supported by both parties - Cisco and VMware.

This is referenced in the vSphere 5 networking guide as it is a unique to UCS -

You can enable DirectPath I/O with vMotion for virtual machines in a datacenter on a Cisco UCS system that has at least one supported Cisco UCS Virtual Machine Fabric Extender (VM-FEX) distributed switch.

Both the Nexus1000v and the VM-FEX solution are there for VM networking and the environment in question should be looked at.

Usually management simplicity along with better performance is where VM-FEX is most applicable.

Environments requiring feature rich functionality (ACL's, netflow, vPath etc) opt for Nexus 1000 solution.

Regarding the updated performance comparisons on VM-FEX, they will soon be posted on CCO.



Manish, when vmotioning a VM in UCS with VM-FEX, I know someone has to temporarily switch from Bypass to Emulated mode, and back to Bypass mode once vmotion is done. Question is: does this switching trigger/occur automatically, or it has to be done manually?

Thanks a lot,

We do not have to do any changes if the port-profile is setup correctly, UCS VM-FEX will automatically do it and if you are doing VM motion of one VM you will not see 0-3 packets loss if there is any network traffic.

problem is in the configuration hints (at least). I have lab with a-fex+vm-fex operational (simple design with 2xC200 w/ P81E, 2xN5K and vCenter. Everything Ok except vMotion. vCenter reports: U cannot migrate VM coz of hosts are not configured for mirgation. Configuration guides for vMotion refers to vswitch which is not correct for VM-FEX (I believe). Cisco's docs have no enought info how to configure neccessary components for vmotion too. Alternative is to make ur own R&D.

Getting Started

Find answers to your questions by entering keywords or phrases in the Search bar above. New here? Use these resources to familiarize yourself with the community: