Windows Server 2012: inside Microsoft's Enterprise Server OS
Storage Spaces are a new form of virtualised storage designed to bring resilient and easily expanded storage within reach of small organisations. There are two key components. A storage pool is a group of physical drives, for which there is no special requirement. You can add and remove drives from a pool, and faulty drives are flagged by the system for replacement. A virtual disk is a volume created on a pool, which can optionally include Raid-like resilience based either on mirroring or parity stripes; however it is not strictly RAID, but a similar technology. Virtual disks support thin provisioning, where the size of the virtual disk is greater than the physical space. The idea is that you add drives as needed when space is consumed. If the pool is completely full, Windows takes it offline until the problem is fixed.