Microsoft has posted to its Building Windows 8 blog details on the next-gen platform's new Storage Spaces feature. Storage Spaces continues the Drive Extender concept from Windows Home Server, allowing the system to pool physical hard drives of various sizes and interfaces to redundantly store data for scale, resiliency, and efficiency.
The system works like a RAID setup but the physical hard drives are grouped into a larger storage pool, which is then split up into spaces. The disks in a pool can be of mismatched sizes and of different interface technologies, such as USB, SATA, and Serial Attached SCSI. New disks can be added anytime while others can be connected but kept on standby only to turn on when needed.
The spaces are virtual disks that function like the physical disks but has more powerful capabilities to ensure redundancy. At least two copies of all data within a space are stored on at least two different physical drives.
The capacity of a virtual space does not necessarily correspond with the total capacities of the physical drives within a pool. The example given is that a "Documents" Space could be set at 10TB whereas the actual physical drives in the "My Home Storage" Pool only has 4TB capacity. This is possible through the magic of thin provisioning, which allocates physical disk storage to a space only when needed and reclaims capacity when files are deleted. This way you can create different spaces that may use the same pool.
This setup ensures data resiliency even if a disk were to fail and is designed to be easy to use. You can still continue to use your current RAID or NAS setup, but this new feature makes everything more integrated into the Windows file system.