RAID is quickly reaching it's technical limits, and imposes major costs on users. It's time to move beyond RAID, and utilize other methods of Software-based redundancy such as Object Storage or Erasure Coding.
- Distributed Object Storage - Items are insteads stored as Objects in Containers. These objects are effectively backed up on many unrelated drives on a case by case basis, configurable based purely upon how much you care about it.
- Ceph - Popular distributed Object Storage system developed by Red Hat. Provides an Amazon S3 compatible API.
- Project Greyhole - Uses Samba to keep things in sync.
- Erasure Coding - Data is encoded in a way that allows the whole dataset to be reconstructed even if portions of it are damaged or lost. This is similar to DVDisaster.
- Logical Volume Groups
- ZFS - http://www.datamation.com/data-center/the-zfs-story-clearing-up-the-confusion-1.html
RAID vs Object Storage
At 4TB, RAID becomes utterly ineffective due to long rebuild times.