After installing Proxmox VE 3.4 with ZFS and raid1 using three disks I get the following pool:

```
root@pve:~# zpool status
  pool: rpool
 state: ONLINE
  scan: none requested
config:

        NAME        STATE     READ WRITE CKSUM
        rpool       ONLINE       0     0     0
          mirror-0  ONLINE       0     0     0
            sda3    ONLINE       0     0     0
            sdb3    ONLINE       0     0     0
            sdc3    ONLINE       0     0     0

```

If I understand the setup correctly all data will be mirrored over three disks. Even though this would support simulatenous failure of 2 drives at once I assume there is a performance penalty to writing everything to two disks. I think two would be enough.

How do I convert sdc3 to serve as a hot spare. I want it to automatically go active and replace the broken disk in case of a drive failure.