[ekidd]

"the suggested default step 1 for MongoDB is to acquire 3 servers?"

At my previous job, we suffered a catastrophic RAID failure. The controller died while trying repair a degraded array. At this point, we valued the data enough that we weren't going to screw around with replacing the controller and restarting the recovery. The whole RAID array went out to DriveSavers, at the cost of several thousand dollars. Now, DriveSavers are really awesome folks, but my goal is to never do business with them again. :-)

After this incident, our policy was simple: If our data mattered, it had to be replicated.

A 3 server configuration is, admittedly, pretty high end: Even if one node is down, you still have redundancy. You can keep the remaining 2 nodes live while rebuilding the failed node.

I know lots of people who care _deeply_ about data integrity, but who keep their databases on a single server. I find this a bit mystifying: Even the most expensive hardware can die in ugly and unrecoverable ways. And RAID arrays are some of the biggest culprits: Their striping formats are usually undocumented and proprietary.