Windows 8 includes a storage scheme suitable for business deployment that can treat hundreds of disks as a single logical storage reservoir and ensures resiliency by backing up data on at least two physical disks.
Called Storage Spaces, the feature sets aside a designated storage area -- known as a space -- for a defined category of data within the entire available disk capacity -- called a pool.
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Pools are treated as single virtual disks that can be partitioned and formatted as if they are single physical disks, according to the Microsoft Building Windows 8 blog. Spaces are defined across multiple physical disks, and the physical disks can still be treated as one even if they vary in size or are connected via different interfaces such as USB, Serial ATA, or serial attached SCSI.
Storage Spaces has advantages that make it suitable for business deployments, writes the author of the blog, Rajeev Nagar, a group program manager on the Windows 8 storage and file System team. "Storage Spaces delivers on diverse requirements that can span deployments ranging from a single PC in the home, up to a very large-scale enterprise data center," Nagar writes.
One interesting feature of Storage Spaces is that it can allocate a space that is larger than the actual available physical capacity of the pool that the space is carved out of. This sleight of hand is done via a technique Microsoft calls thin provisioning, which keeps data from overflowing the space by freeing up capacity whenever files are deleted or an application decides that such capacity is no longer needed, according to the blog.
This makes it possible, for example, to create a 10TB space within a 4TB pool, Nagar writes.
Anything stored in a space is mirrored on a separate physical disk. "Resiliency is built in by associating the mirrored attribute, which means that there are at least two copies of all data contained within the space on at least two different physical disks. Because the space is mirrored, it will continue to work even if one of the physical disks within the pool fails," according to the blog.
Storage Spaces has a second resiliency feature called parity in which some redundancy information is stored next to data in a space, so if a disk fails, data can be reconstructed automatically. "While conceptually similar to mirroring, parity-based resiliency utilizes capacity more efficiently than mirrored spaces do, but with higher random I/O overhead. Parity spaces are well suited for storing data such as large home videos, which have large capacity requirements, large sequential (predominantly append) write requests, and an infrequent-to-minimal need to update existing content," Nagar writes.