Last week I read a few interesting articles about storage in desktop virtualization, VDI in particular. The consensus is that this storage belongs on local disk, not the SAN. One industry expert even says you can use SSDs locally and still get away for less money. I beg to differ.Blogger Brian Madden posted an article making the case for using local disk. Madden makes some good points, so kudos for starting a needed conversation. Industry veteran Ron Oglesby followed Madden's post, going one step further and suggesting that we can even use SSD and it will still be cheaper than SAN.

But I think they're missing a key point.

When talking local disk vs. SAN for desktop virtualization, the first thing that comes to mind for me is, Why are we even comparing these two technologies? Are we trying to save on CapEx expenditures to justify the project? If so, both Brian and Ron know very well that VDI does not deliver significant CapEx savings. Desktops have no data center footprint and have always been a decentralized model.

Desktop virtualization, however, will save you significant money on OpEx, which is where the highest spend tends to be. CapEx costs have been steadily going down and represent less than 20% desktop total cost of ownership, according to Gartner, IDC and others; meanwhile, OpEx costs have been steadily going up and represent more than 80% of total cost of desktop ownership.

Beware trying to justify a VDI project by showing savings in CapEx just to get it approved. You may well create an administrative nightmare in which you spend more in operational and management costs than you saved. And no, you can't hide that from the CFO for very long.

Rather than comparing local disk to SAN, then, we should be comparing how much it will cost us to refresh these desktops vs. the added SAN capacity. If you have to refresh desktops, then you must have money allocated somewhere. So let's look at the numbers.

Desktop Refresh Consider a midsize company that has about 2,000 desktops. To keep the math simple, I am going to assume each desktop will cost $500 to refresh, hence: