I recently read an article in CIO magazine about the cost per gig per month. In the article they quoted Google at about 6 cents per gig per month.  I use Amazon for a few projects, which runs at about 12 cents per gig per month.   Including labor and hardware I decided to look at about what it would cost per gigabyte per month for Xsan storage.  Averaging out 30 installs that we did over the past year turned out a total of about 7.2 cents per gig per month, as opposed to around $2.00 per gig per month which is pretty average for many SAN solutions.  Now, Xsan does have its drawbacks compared to a lot of other truly enterprise-class storage solutions (no snapshots, no LUN redundancy, etc), but provided you build it properly, use it for the purposes that it is actually intended and therefore keep labor costs down over a 3 year cycle you can get similar TCO numbers to what you might end up paying for other solutions.  

Having said this, the larger Xsans typically require more infrastructure and features, which can lead to around double the cost per month per gig.  For example, introducing Cloverleaf or Vmirror into the equation will typically require us to double up storage costs and require bigger and better switches. 

I will not say that a cloud storage service such as Google or Amazon doesn’t have its place.  It absolutely does: offline storage, web storage, if you have an existing Xsan and need to archive but can’t spring for the tape drive, Final Cut Server archival (see my previous post on using that) if you travel a lot (like me), etc.  But before you jump on the Storage as a Service bandwagon run the numbers very carefully.  If it makes sense on a per-use basis then absolutely go for it, but try and factor everything in the process (especially the data access speed over your WAN pipe and additional load that will be placed on said pipe).