NFS is Slow

I have done more testing the MyBook is fast when using NFS.  The only time is seems to run slow is when I am using it as an NFS mount for VMware ESX.  I would like to back my environment up to the drive via NFS.  I have tried two different ESX hosts both can copy a 1GB file to my macbook over NFS in about a minute but to the MyBook takes more like 10 minutes.  I realize this might not be a supported configuration but I just can’t understand why this is happening. 

ESX01 ----> 1GB NFS Copy to MacBook hosting NFS ~ 1 Min

ESX02 ----> 1GB NFS Copy to MacBook hosting NFS ~ 1 Min

ESX01 ----> 1GB NFS Copy to MyBook hosting NFS ~ (10 Min)

ESX02 ----> 1GB NFS Copy to MyBook hosting NFS ~ (10 Min)

MyBook ----> 1GB NFS copy to MacBook hosting NFS ~ 1 Min

MacBook —> 1GB NFS copy to MyBook hosting NFS ~ 1 Min

Any ideas are welcome.