The Storage Layer
The storage layer or infrastructure is an extremely important component of IT service. The storage layer provides space (capacity) for storing data, as well as stored data access and data sharing, and overall storage management, as depicted in Figure 12.
Figure 12 Data storage infrastructure functions.
Computer data is typically stored on hard disk drives for fast retrieval, though tape and optical disc may be used to store older, less frequently accessed data, or copies of data for backup purposes. The storage infrastructure is designed, or architected, to ensure that the right mix of primary (disk) and secondary (tape or optical disc) technologies are provided.
To increase storage capacity beyond that of a single disk drive, multiple disk drives are often configured into a larger storage array. To a computer, the array may look like an extremely large disk drive, or it may be divided into several very large "virtual disks."
Arrays also frequently offer internal technologies for data protection through redundancy, as in the case of redundant array of independent disks (RAID) arrays. Some also provide additional technologies, such as array mirroring, used for copying data from one array to another as it is being recorded. Mirroring provides a stop gap against disaster: if one array fails, its mirror array, if properly configured, can replace it instantaneously, and IT services can continue to be provided.
Much more can be said about storage, including the application of technologies such as network-attached storage (NAS) and storage area networks (SAN), and the storage infrastructure is explored in greater detail later in this book. For now readers need to understand that the storage infrastructure is key to the performance of IT services, so much so that a class of service providersStorage Service Providers or SSPshave begun to appear in the marketplace. SSPs offer managed storage as a service. More on this later.