Disk space optimization with the Agent for Hyper-V

Last published : Apr 02, 2026
Backup Exec attempts to perform disk space optimization during Hyper-V backup jobs. Disk space optimization is performed whenever possible.
However, disk space optimization cannot be performed in the following situations:
  • The file system is not NTFS. For example, if the file system is FAT, ReFS, or Linux, then disk space optimization is not performed.
  • The disks are configured with Windows Storage Spaces.
  • The volumes are configured with dynamic volumes, such as spanned, striped, mirrored, or RAID 5, for either MBR or GPT disks.
  • The vhd file or vhdx file is not consistent at the time of backup.
A file may not be consistent for the following reasons:
  • If an offline backup of a running virtual machine is performed. This may occur if the Hyper-V Integration Services are not installed or if the version of Integration Services running on a virtual machine do not match the version running on a Hyper-V host. This may also occur if the virtual machine runs an operating system that is not supported.
  • The user-created checkpoints (snapshots) do not generate consistent disks.