Is there a best practice guide or document in regards to sizing datastores in esxi 5.1?
Welcome to the Community - really sizing the VMFS datastore is going to depend on the size requirements and the loads that will be placed on storage - fro best practices info you can check here - http://pubs.vmware.com/vsphere-55/topic/com.vmware.ICbase/PDF/vsphere-esxi-vcenter-server-55-storage...
I have also moved this to a more approrpiate forum
It depends on the environment that you have like Weinstein mentioned.
Here's a link for vSphere 5.1
http://pubs.vmware.com/vsphere-51/topic/com.vmware.ICbase/PDF/vsphere-esxi-vcenter-server-51-storage...
