| What Is Storage Virtualization? Storage virtualization is the logical abstraction of storage from its physical deployment and configuration. By hiding the complexity of physical storage, virtualization greatly simplifies and reduces the cost of storage administration. RAID is a low-level virtualization implementation. Storage virtualization enables efficient utilization of storage capacity. Virtualization enables nondisruptive changes to the back-end storage network. Both RAID and JBOD storage can be incorporated into the same storage pool. Virtualization can be extended over distance via SAN extension or IP storage. Available products may support only low-level virtualization functionality. In-Band and Out-of-Band Virtualization Metadata is information about how data is stored on disk and how disk assets are organized. In-band virtualization sends metadata and data over the same network path. Out-of-band virtualization separates control metadata and data and sends them over different network paths. In-band solutions are unintrusive to both hosts and storage targets, but they may create performance bottlenecks. Out-of-band solutions avoid performance bottlenecks, but they require software drivers on each server. An in-band virtualization engine can reside in a third-party appliance or can be incorporated into a SAN switch. Host-Based Storage Virtualization SAN Interconnect-Based Storage Virtualization Interconnect-based virtualization is transparent to hosts as well as storage targets. Interconnect-based solutions can support heterogeneous multivendor environments. For high availability, redundant virtualization engines are required. Interconnect-based solutions must provide adequate performance to avoid becoming bottlenecks to data throughput. Storage-Based Virtualization Storage arrays provide virtualization functions such as RAID and disk-to-disk data replication. Storage-based virtualization may allow storage pools to span multiple physical arrays. Storage-based virtualization is inherently proprietary, limiting its appeal to single-vendor shops. Multivendor Storage Virtualization File Systems and NAS Virtualization Metadata from separate file systems can be combined to present a larger, virtualized file system. File system virtualization requires software on each host system. Virtualization of file systems can be combined with virtualization of block storage resources. Tape Virtualization Tape virtualization relies on in-band intervention between backup servers and tape subsystems. Tape virtualization is transparent to servers and tape devices. Tape virtualization enables efficient use of tape drives and tape media. Virtualization and the Data Storage Utility Storage as a utility requires application-aware, policy-based virtualization intelligence. Different types of data may require different methods for storage placement. Automated policy engines can be used to enforce data placement, quality of service, performance, availability, security, capacity, and other requirements. In addition to intelligence, the ideal of data storage utility requires support for multivendor environments. |
