I'm currently running 2 old desktops stuffed full of HDDs and a new i3 machine.
1) Pentium 4, 4g ddr POS, 6x2tb storage and a tiny OS disc.
2) Older core i7, 8g ddr2, 6x2tb storage and tiny OS disc.
3) i3 machine, 32g ddr3, 16g ssd for OS, 500g for VMs.
Usable space is about 7tb. Server #2 mirrors with server #1, the machines each run raid 5 with a hot spare... overkill but I've lost data enough times to be completely done with that mumbo jumbo. I'll soon be adding storage to #3 and moving #1 off site and mirroring remotely. I run a mix of debian/fedora/other. Between server #2 and #3 I have 6 VMs.