How to properly configure load balencing in ESX 4i

Unless you have Cisco EtherChannel with trunking you are not going to get true load balancing.  It does a type of round robin and it provides failover.  The round robin is per VM.

This is two sided- most of the load balancing is per flow, even with cisco devices.  With per flow balancing when you start the file copy it is only 1 flow.  I feel obliged to say that with the management nic on esx servers (which is used for the copy) they really only use 1 of the nics for most traffic regardless of configuration.  Also realize you are using NFS for the file copy, ESXi has a funny stack for dealing with NFS that can be slower.  

namoon: Good point but with NFS I've actually had faster responce then with iSCSi, I believe most of that is due to overhead of iSCSI vs native file level througput and scsi locking.  Per flow on iSCSI has been upgraded on ESX 4 with multipath and severak vmkernel ports, so no longer do we have to deal with a max. of 1GB throughput no matter how many nics we have.

rdefino:  If it was working before take a look at the other side.  Copy the same file from a physical server to your destination, it could be several issues that are not related to ESX.