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. Storage in a pool is then distributed among one or more spaces. Each space can have its own redundancy policy, with three kinds of fault tolerance offered: 2-way mirroring, 3-way mirroring, and RAID 5-like parity. With the mirrored options, a space’s data is stored either twice or three times within a pool. With the parity option, the system will compute additional information and store this within the pool. If any disk in the pool fails, the data can be reconstructed using this additional information.

Spaces can be thin provisioned, allowing the creation of spaces that are larger than the underlying pool. This allows potentially simpler management—a large “media” space for TV shows and movies could be created with some large size, say 50 TB, with only 2 TB of physical capacity in the pool. As more shows are recorded or downloaded, and space becomes tighter, additional drives can be added to the pool; the space will then use this extra capacity with no further configuration required. The new technology is far better integrated into the core operating system which makes it robust enough for mainstream use. The blog post implies that Storage Spaces are ready even for enterprise workloads, making mention of the ability to scale up to “very large-scale enterprise datacenter(s)”, with pools made up of “hundreds of disks”—not a promise anyone would make of the home user-oriented Drive Extender. The company says that guidance will be offered on how to partition disks so that a partitioned boot disk can be added to a pool, but that straightforward booting unfortunately won’t be possible. Storage Spaces will be a feature of both desktop and server editions of the operating system.