Volumes

A volume is a logical disk that the system presents to attached hosts.

Application servers access volumes, not MDisks or drives. To keep a volume accessible even when an MDisk on which it depends has become unavailable, a mirrored copy can be added to a selected volume. Each volume can have a maximum of two copies. Each volume copy is created from a set of extents in a pool.

You can create different types of volumes, depending on the type of topology that is configured on your system. For example, in standard topology, which is single-site configuration, you can create basic, mirrored, or custom volumes. If you have a HyperSwap® topology, which is two-site configuration, you can create basic, HyperSwap, or custom volumes. For each of these volume types you can specify specific details, such as a method of capacity savings for the volumes. The system supports compression and thin provisioning to save space on volumes. With compressed volumes, data is compressed as it is written to the volume, which saves capacity on the volume. Thin provisioning creates a volume with more virtual than real capacity that allows the capacity to grow as it is needed. Only Storwize® V5030 models that have installed additional memory module (16 GB DIMM) support compression.

The system uses base-2 (binary numeral) as capacity indicators for volumes, drives, and other system objects. The management GUI and the command-line interface (CLI) use different abbreviations to indicate capacity, but the value for these capacity indicators is the same.