All Proxmox VE versions do not support Linux Software RAID (mdraid). That means, it's not tested in our labs and not recommended, but it's still used by experienced users. If you want to run a supported configuration, go for Hardware RAID or a ZFS RAID during installation.
- Proxmox VE 2.x supports Fake RAID (BIOS RAID), but not since Proxmox VE 3.x
- Proxmox VE since 3.4 supports Software RAID if you choose Storage:_ZFS
If you still want to use mdraid, you can create the required RAID level during Debian installation and then install Proxmox VE or create RAID after install Proxmox VE. Look at the external links below and the following pages:
- Install Proxmox VE on Debian Squeeze
- Install Proxmox VE on Debian Wheezy
- Install Proxmox VE on Debian Jessie
- Youtube video: Setting up simple software RAID-1 on Debian 5