I have a proxmox 3.x Server more than two years on a single node, a PX60 Server with three Debian Linux VMs in production use (Mailserver, Groupware SOGo, Kivitendo, Webhosting....) with mdadm Software Raid 1. Next Step is to change to Proxmox 4.x and ZFS.
Everything works very stable and fast.
maxprox