unallocated space on backup drive

Hi,

Am using SBS 2011 - have an external drive with backups on it (Server Backup), the drive has corrupted etc and on inspecting it through active partition the data is there but it shows the drive as unallocated space, I need to do a bare metal restore, what is the best way to do this, without destroying the data

The drive has only ever been used as a backup drive on the server

Any help would be appreciated

Thanks in advance