MANAGING STORAGE AND MIGRATION OF BACKUP DATA

A method and system for client backup data management and storage using virtual tape libraries (VTLs). A VTL controller executing a software method receives metadata that distinguishes among a plurality of different versions of backup data. The VTL controller determines a latest version of the backup data. The VTL controller determines a migration set of zero or more versions of the backup data. The latest version and any version included in the migration set are included in the plurality of different versions. The VTL controller determines that a storage of the latest version in a first storage medium (e.g., magnetic disk) of the VTL is complete. The VTL controller migrates the migration set to a second storage medium (e.g., magnetic tape) of the VTL if the migration set includes at least one version of the backup data.