Slow vStorage Migration on 10G network - 30MB/sec max

• ESXi 4.0U3 server with 10G Intel x520-DA (82599) cards, Intel Nehalem 2.9G QuadCore CPUs, 32G RAM, USB boot drive

• The ESX server has a single vSwitch using a single 10G NIC configured for 9000 MTUs (both the VMKernel and vSwitch ports)

• Two NFS servers with 10G Intel x520-DA cards, LSI 8888ELP RAID Controllers, Intel 2.3GHz CPUs, 4G RAM, CentOS 5.7, 12x1T drives in RAID-6.  The servers can read/write at +400MB/sec across NFS mount points (using async options)

• Cisco N5010 10G network switch (no VPC) with jumbo frames enabled

• From the ESXi CLI, I can do a copy from one NFS datastore to another at > 100MB/sec

• From the ESXi CLI, I can do a "wget" from one NFS server to /dev/null at +400MB/sec (wget http://nfs1/file1 -O /dev/null)

• From the ESXi CLI, I can do a "wget" from one NFS server to another nfs mount point at +125MB/sec (wget http://nfs1/file1 -O /vmfs/volumes/nfs1/file1)

• A VM running on one of the NFS data stores can perform a local write at > 100MB/sec using "dd" (dd if=/dev/zero of=file1 bs=1M count=1000)

• Running iperf between the NFS server gives >900MB/sec network performance (no packets loss)

I have been doing tons of testing and have narrowed the problem down to the storage migration function.  Although the ESXi servers can read and write from the network and NFS servers at >100MB/sec, the storage vMotion tool only gets 30MB/sec max speed.  My test VM is a CentOS VM with a 40GB thick-provisioned VMDK (powered off during storage migration), and there are no other VMs running on the ESXi server.  I have fully patched both the NFS and ESXi servers, and I have even loaded the latest Intel driver package from VMWare ("ixgbe" driver 3.4.23) installed on both ESXi servers.