I can’t tell you how often we are asked this question and the answer has many variables including the amount of aggregated I/O of the servers being virtualized onto the datastore, the storage protocol used in connecting to the datastore, etc.
I believe Duncan Epping at Yellow Bricks has provided us with a simple answer to this traditionally difficult question. Hopefully you’re very familiar with Duncan, he’s an active contributor to the VMTN and his site is one of the top VMware blog sites that is always brimming with the type of information that can significantly improve your VMware deployment.
I compliment Duncan on the way he phrased his guidance. I believe we may want to consider rewording the recommendations currently in TR-3428 (VI3) and the upcoming TR-3749 (vSphere). BTW – the current guidance in both of these documents is a LUN ranging in size from 300 GB – 700 GB.
Go check out Duncan’s post, it contains very solid guidance to this long running question, and may I suggest you drop him a note for his thoughts on sizing a NFS datastore.