The thread discusses expanding a RAID 1 mirror by adding more hard drives, with advice suggesting that while it is possible to add more disks to the mirror, using RAID 5 or RAID 10 would be more efficient for increased storage or performance. The original poster confirms they are using RAID 1 for disk mirroring. Other contributors recommend RAID 5 or RAID 10 for better redundancy and performance benefits. Overall, the discussion highlights options for expanding or optimizing RAID configurations on Windows systems.