Windows Home Server NAS: HDD vs Drobo

"But what happens if the Drobo dies? (Which, by the way, is much more likely than an off-the-shelf WHS box dying, in my experience.)

Just keep it simple. Get something like an HP MediaSmart Server and use its built-in drive bays."

I'm successfully using a Drobo with Windows Home Server. I describe the experience here. I made this choice because it saves hard drive space. It also provides more stability for my system backups. With WHS all files you want backed up are duplicated and thus use 2x the space. With the Drobo, only 1 drive in 4 is used for parity. Additionally, WHS places the system backup files on only 1 drive so if any hard drive fails, you risk losing your imaged backups (but not the files you specifically mirror).