Take a look at this blog from Chad: [URL]  Thin on thin - not an issue
Hello   I read some recommend not to have thin on storage and thin on vmware same time , is there any known issues on this ?      about Chunks and Fast on VNX  since movements depending on number of IOs and 1 GB chuncks are moved  how does fast help since luns are distebuted and what if IOs are high on small part of storage but IOs in total dont seem to be high for the 1 GB Chunk ?  I am not sure about that idea I guess 
Thin for VMWARE and Storage , and question about Fast and Chunks