We do not recommend running SmarterMail on a remote file system. It's possible, and you can specify UNC paths for locations, however there will be a decent performance impact due to the overhead of these protocols. We recommend a RAID1 only for the OS installation, and rely on a RAID10 with 4 drives minimum for the mail volume.
If you wanted a true storage solution we've worked with Nimble and thoroughly tested their solutions with SmarterMail and highly recommend their platform due to the IO and backup capabilities. We can provide you models and general guidelines on costs for your needs. Just let us know if you would like more information and we will be glad to assist further.