My home server has had a Christmas present. It now contains four Western Digital Red 2.5" hard disks (they're the special edition designed for NAS and RAID usage), hooked up to an Adaptec 6405E RAID card.
This is a proper hardware-based RAID card with a 128MB cache, albeit one without the necessary processing power to compute RAID-5 parity. However, RAID-10 is good enough for what I want.
The performance is impressive (in my opinion). Read speeds of ~250MB/s and write speeds of ~150MB/s. This is about probably about 30% faster than the software RAID-5 I was running before, and that's with 5400rpm disks rather than 7200rpm.
The installation process involved commandeering my desktop PC as a temporary server onto which I installed a copy of Proxmox VE and moved the VMs onto it. I'm not brave enough to risk clustering and hot migration just yet. I then installed the new RAID array into the server and did the same process in reverse. The key servers were down for an hour or so each, although shifting 380GB of music and photos in each direction did take quite a while (all day in fact).
The revamped server is still eerily silent despite containing 5 hard disks - I added a 750GB 2.5" disk for easy daily backups - and me having plugged in an extra case fan to ensure the RAID card doesn't overheat. The card has a small heatsink on it, which helpfully points downwards when it's installed in a regular tower case, so having a bit more air wafting gently over it will definitely help.