SAN Volume Controller (SVC)

Deployed as x Server-based node pairs, the IBM SAN Volume Controller (SVC) is a combined software/hardware offering that provides a virtualization layer between the physical disks of a SAN (called Managed Disks, or MDisks in IBM literature), and the individual hosts that access them. When hosts access the storage through the SVC, they see a list of virtual SCSI LUNs (VDisks) that the storage administrator has defined. These virtual LUNs are in turn mapped to the physical SAN storage arrays; I.E., the SVC acts as a host to the storage arrays themselves.

This virtualization layer provides the storage administrator with multiple benefits, including the ability to manage multiple, heterogeneous storage arrays from a central interface, with all physical storage made available through a single virtualized storage pool; the ability to manage physical storage online without disrupting applications (data migration tools enable the SVC to move data to and from physical disks without blocking I/O access to the virtual disks that hosts use, and virtual disk capacities can be altered as needed from the physical pool); and the ability to tier storage access based on performance or other organizational needs (by grouping specific types of storage or arrays into separate virtual entities). Each host server can be presented with its collection of available virtual disks, and a special configuration mode exists that allows existing physical disks to be mapped in a one-to-one relationship to virtual disks; a feature that the vendor states enables the importation of non-virtualized data into the virtual scheme without requiring the migration of data physically from one device to another. Up to 1,024 host servers can be supported by the platform.

Other features include automatic discovery of existing physical disks and optional functionality (priced separately) for metro (synchronous) or global-scale (asynchronous) data mirroring and FlashCopy - a copy-on-write-based snapshot tool that allows for the background (network-based) copying of data across storage systems and tiers.

Management of the platform is via the vendor's IBM System Storage Productivity Center (SSPC), which is also served in a combination hardware/software platform and provides a GUI for the creation, mapping, and management of VDisks, among other features. The SSPC can manage multiple SVCs as well as the vendor's DS8000s.

IBM's site lists multiple arrays, switches, and hosts as compatible with the platform, including selected EMC CLARiiON and Symmetrix, Hitachi, Sun StorEdge, HP, and IBM TotalStorage ESS arrays; selected Windows (2000/2003 and now 2008), Linux, VMware, AIX, and Solaris hosts; and selected Brocade, McDATA, Cisco, and CNT SAN switches, among many other supported platforms. See the vendor's Web site for current details.

New features in the latest release of SVC include:

- Support for thin provisioning; virtual disks now only use space when they are written to (as opposed to reserving all needed space when they are allocated), and FlashCopy uses only the space needed to store changes between the source and target data

- Support for virtual disk mirroring (copies of a virtual disk on different systems)

- Support for Windows 2008 and Mac OS X Server hosts, and Pillar Axiom disk systems

The IBM SAN Volume Controller is available now; the new features are expected to be available on June 27, 2008. An entry level package (dual SVCs, dual--and required--UPSs, the SSPC, and the SVC software licensed for use with 1 TB of capacity) is priced at $50,000.

Contact IBM for further information.