## How Backup Works

Active Backup for Business performs VM backup following the process below:

1. When a new backup task starts, Active Backup for Business connects to the virtualization hosts and requests vCenter Server or ESXi host to create a VM snapshot. VM disks are put to the read-only state, and every virtual disk receives a delta file. All changes that the user makes to the VM during backup are written to delta files.
2. If application-aware backup is enabled for the backup task, Active Backup for Business connects to VM guest OSes, deploys runtime processes on VM guest OSes and performs in-guest processing tasks.
3. Active Backup for Business reads the VM data from the read-only VM disk and transfers the data to the backup destination on Synology NAS through network transfer mode. After the first full backup, in the following incremental backup (only with CBT enabled), Active Backup for Business uses VMware CBT to retrieve only those data blocks that have changed since the previous backup time. If CBT is not available, Active Backup for Business will perform full backup.

While transferring VM data, Active Backup for Business compresses source VM data and encrypts the data during on-flight transfer and then send it back to Synology NAS. After the backup proxy finishes reading VM data, Active Backup for Business requests the vCenter Server or ESXi host to commit the VM snapshot.