In other words, should I leave a spare disk on the shelf or set it up as a hot spare?
If the server has a little bit of downtime, it isn't the end of the world. It's not a webserver or anything that needs to serve stuff up 24/7. Are there any downsides (drive life/wear, etc) to keeping the extra hard drive set up as a hot spare or is it better to leave it packaged on a shelf somewhere if I don't require the immediate recovery time of a hotspare?