Everything you always wanted to know about VDI but were afraid to ask (no, it's not an STD)
All you need to make virtual desktops go
Scenario 1: Designing for a knowledge worker
Consider for a moment the standard "knowledge worker": someone on the end of a string typing away into a word processor, answering instant messages and occasionally browsing the web. If you hand him or her a non-persistent desktop then update storms over the network aren't an issue; the only real storage traffic you're going to see is during logon and logoff.
Here, write caches – be they at the array or host-based – are your best friend. You can fill up the SSDs in the write caches during logon and logoff and they can sit there and drain to the storage for the rest of the day. This is the exact scenario in which they excel. Atlantis' ILIO, PernixData's FVP, hybrid storage arrays (Tintri, Tegile, Nimble) and server SANs (Maxta, Nutanix, VSAN, etc) could all be of use here.
This isn't to say that other storage technologies won't have an effect. Host-based read caches (VMware's vFlash, and Proximal Data's AutoCache) are an example of a technology that will be of some help handling the logon/logoff spikes, even if not quite so much as other write cache solutions. Still, read caches are comparatively cheap and can be slotted into existing infrastructure. As such they are also worth a look for this scenario.
If all your users log on at the exact same time then write caches will pay for themselves in short order; they will prevent your staff from sitting and waiting for their desktop to appear. If, however, your staff logon in a somewhat staggered fashion over the course of an hour then you can probably get away with a host-based read caching solution and save yourself a ton of money.
Deciding what to use becomes a "bang for your buck" calculation. This is where understanding your users and their use patterns will make a big difference. How much are you willing to spend, and what kind of logon/logoff performance do you really require?