Introducing the Agent › How the Agent Analyzes Data that Resides on Virtual Machines

How the Agent Analyzes Data that Resides on Virtual Machines

Virtual machines (VMs) running VMware vSphere and Microsoft Hyper-V can identify the used blocks of data on virtual disks. This capability lets Arcserve Backup decrease the overall backup time for jobs. The overall backup time decreases because Arcserve Backup backs up only the used blocks of data, not the entire disk.

Arcserve Backup uses the block analysis approach when backing up data that resides on Hyper-V VMs, and on VMware VMs that have VMware vSphere Web Services SDK and VMware VDDK running in the environment. In addition, change block tracking must be enabled on the VMware VMs. For more information about change block tracking, see the VMware website.

Note: On VMware VMs, you must specify a backup approach. For more information, see Specify a Backup Approach.

When backups of VMs run, Arcserve Backup backs up only the active blocks relating to the full backup phase of Raw (full VM) backups (with and without the Allow file level restore option specified), and Mixed mode backups with the Allow file level restore option specified.

Be aware of the following behavior:

• On Hyper-V VMs, Arcserve Backup does not use the active block analysis approach to backups when the agent cannot create disk bitmaps of the VM. The agent cannot create disk bitmaps when the parent virtual hard disk (VHD or VHDX) is a fixed disk and not a dynamic expanding disk. If the agent detects this condition, Arcserve Backup reverts to previous backup behavior, which is to analyze each block of data contained within the backup.