In the early days of VDI, storage immediately became a pain point in any virtual desktop implementation using a SAN. Basically the only way to get the IOPS up to an acceptable level was to add more disk spindles, regardless of whether or not more storage space was actually needed. More recently hybrid arrays have become all the rage that use fast SSD caching to cache common reads and often buffer writes before it gets written to the traditional spinning drives. The prices on hybrid arrays are often also extremely competitive with traditional arrays and way cheaper than going all flash....
So simple decision right? Go hybrid and problem solved?
Not so fast..... VDI isn't the same beast as serving databases and web pages.
I have personally seen instances, due to the write "IO blender" effect of hundreds of virtual desktops doing many different things, effectively flood and fill the SSD's of a hybrid array with writes which resulted in the overall performance of the array to fall dramatically and caused latency to increase as the array struggled to flush the SSD cache to spinning disks (so we're back to the original problem) in an effort to free space to cache more writes.
My thoughts on a true solution? Well I think I've found a few.... and which I'll soon post about each separately in the future.