I'm trying to find out what I'd need to do to enable a RAID 5 setup where I really could swap out a disk while the system was still running.
I'm trying to figure out where to start on this. I assume I'll use one of those caddies, so that I don't need to open the case when I want to change a drive. Does the ability to do this depend on the caddy, the controller, both?
I'm not looking for hotswap meaning the ability to mount a completely different disk the way you can with a USB drive. If I set things up correctly, the OS shouldn't even know that anything is happening, or even necessarily that I'm using RAID at all.
I wasn't quite sure what to Google for, so I'm asking here. Thanks!
RAID is not designed to swap storage volumes on the fly. For RAID, "hot swap" means to replace a failed drive with a new, working drive so that the RAID controller can rewrite the redundant data or parity information to protect against the next failure. From the point of view of the OS, it's supposed to look as though the RAID volume was online and working just fine the whole time.
If you want to swap storage volumes (ie, remove the "movies" volume and plug in the "songs" volume), what you want is an external disk in an eSATA or USB-connected enclosure. RAID will not do that for you.
Part of it depends on the RAID controller - they all have their idiosyncrasies but most of them should automatically rebuild if a different drive is plugged in.
If it's just the "hot swap" part that you're concerned about, then the actual SATA connector is designed for that, so you should be able to do it with any drive. Of course if you have a standard case then you'll have to open up the system while it's running to do that, and that risks disturbing other drives.
If you want something more elegant, you can buy drive caddies and mounts that fit into external 5-1/2" slots in a standard computer case, or you can buy an external tower that's specifically designed to hold hot-swappable drives - the latter is typically a NAS (Network Attached Storage) unit that has it's own processor and RAID controller.
One thing to be very careful about is how your identify which drive is which. If you have several drives in a failed RAID-5 set, the last thing you want to do is to try to pull out the dead drive and get the wrong one.