Volume Shadowing
Volume Shadowing is a System Integrated Product that implements a RAID Level 1 storage strategy (sometimes referred to as disk mirroring) to provide data availability for disk devices. It maintains redundant copies of data on a collection of disk volumes called a shadow set: if one of the disks in the shadow set becomes unavailable, the data remains accessible; reading performance is also enhanced.
Volume Shadowing for OpenVMS is included in the High Availability Operating Environment (HAOE) media kit.