Reality check — reliability

When the goal is reliability, it’s a self-defeating approach to mix and match hard drives. A flaky drive might be tolerated by the Drobo, but then again there might be a problem. It all gets back to how cheap new hard drives are, new hard drives matched in capacity and speed.
The Drobo is a real busybody, and even when you are not using the drive, the Drobo often continues doing whatever housekeeping it needs to do: this puts extra stress onto drives, including extra heat stress. And it’s annoying when things ought to be quiet.
If you’re after reliability, get new enterprise-grade drives (here’s one good choice), and get a quality enclosure that also offers high performance, such as the OWC QX2.

Reality check — performance

The performance of the Drobo stinks.
I’ve never seen a slower Firewire 800 enclosure, and that’s using the Drobo with the fastest SATA drives I’ve yet tested, the 2TB Hitachi 7K2000. You can do better with a good USB thumb drive! It’s not unfair to say performance is pathetic.
Here’s kicker: when a drive fails, Drobo performance is cut by another 60-80%, down as low as 7-8MB/sec in my testing. That means a single Canon 5D Mark II RAW file might take ~3 seconds just to read on the Drobo eg 6 seconds to duplicate. Not usable.

Performance — a new low

I didn’t have a week to let my usually DiskTester fill-volume test run. That’s about how long it would have taken with four 2TB drives installed.
Using Firewire 800 on a MacBook Pro 2.93GHz with Snow Leopard 10.6.1, the Drobo writes at 19-22MB/sec and reads at a leisurely 29-32MB/sec. Some USB thumb drives do better than that!
Just about any other Firewire 800 enclosure (including the OWC QX2) will write at least twice as fast, and read at least twice as fast. Firewire 800 is relatively slow to begin with, but the Drobo finds a way to degrade it to USB speed

Backup

Data Robotics tells its customers that the Drobo protects their data (it does), but the Drobo can fail too, and backups are mandatory. Yet the Drobo is so slow that backing up is infeasible once you pass 500GB or so.
With a high-capacity Drobo; think in terms of days just to read the data, let alone write it to a backup drive. That’s assuming there are no glitches and you can continue using the Drobo while backing it up. Restoring a lot of data to a Drobo? How many hours or days are you willing to wait for you business to be down?
And you had better have a backup; the Drobo can fail like anything else. The Drobo is not a backup solution, it’s a reliability solution. Use a simple and cost-effective backup strategy.
A device that can’t be backed-up or restored in a reasonable amount of time is a recipe for disaster.
Drobo marketing literature suggest keeping whole sets of drives from the Drobo for backup, which implies you need two Drobos: one main unit and another backup. But only one backup is negligence for professionals, two backups, stored offsite, should be considered an absolute minimum, and three or more, rotated regularly, are strongly advised.
Re-read the performance section for how infeasible Drobo backups are (with any substantial amount of data). Not to mention a lot of money wasted when far cheaper and faster alternatives exist that don’t require multiple drives for a backup set.
Data recovery if a Drobo fails might run into the 5 figure (yes five figures) at a place like Drive Savers, so save your pennies. I don’t see any data recovery discussion on the Drobo web site. Be sure to ask, and compare to what a vendor like OWC offers for their enterprise solutions