Hi Paul,
there are multiple factors that you should take into account, but if you consider performances only, you may want to use the following pointers to base your decision on:
- SAN has a higher throughput/lower latency than NFS in nearly all cases. The cases where you would actually consider using NFS above SAN are are when you need typical NFS functionnalities (eg.: very very fast data recovery, in minutes) or when you are not concerned with lower perfomances (for instance, you don't have a lot of VM's accessing your NFS simultaneously, or you have low I/Os).
- Web servers tend to do many many small I/O requests, which would make them the best candidates to become NFS clients (NFS tends to be better than SAN for small I/Os).
- From a functional point of view, do consider the single point of Failure you are going to create.
- Consider caching mechanism: I have no idea what kind of data you are accessing on disk, but the caching mechanism may be different (will be different) if you access the data locally ( from the point of view of the Guest operating System) or remotely (over an NFS or CIFS Link).
- The kind of performances you will get largely depends on the type of NFS server you have (Idon't see it in your post); you do want to read the specs, an don't try it with anythin else than an appliance, you'll be sorry.
In short: If you consider it for the performances, don't bother: you're good. If you want to do it for other reasons than performances (manageability, ...): measure the disk throughput you have, tranlate this to network traffic + overhead and compare with the infrastructure you have. Plan a test, see how it behaves, dont forget to load the webserver a bit ;-). If all goes well, migrate the rest of your farm.
Hope this is the answer you were looking for.
