After the transparent snapshot creation operation is complete, you can initiate a delta sync operation or an incremental operation (see Figure 12). The process is as follows:
- PowerProtect Data Manager issues API calls to vCenter for a delta sync operation and provides the previously created snapshot UUID.
- PowerProtect Data Manager signals to TSDM to start the delta sync flow through vCenter API, which resolves the relevant ESXi host.
- The TSDM uses VAIO APIs to query and track the changed areas that the transparent snapshot bitmap represents.
- For each changed area, the data is read from the disk.
Note: The delta sync operation uses a Fast Copy overwrite approach. In this approach, the previous point-in-time files are first fast copied. The fast-copied files are partly overwritten with the incremental data. Only the delta or changes that are represented by the currently synced snapshot are copied. These changes are copied in the Snapshot Extent Store (SES).
- The changed data or delta is read from the disks to create a consistent data flow.
- The read data is written to protection storage using the DD Boost library.
- The changed data write to protection or secondary storage is now complete.
- When all data has moved to protection storage, the TSDM sends an acknowledgment to the ESXi host that the operation is complete. The vCenter level task is marked as complete.
- The metadata is written to protection storage. In this step, the VM metadata (such as VMX files, manifest, and the last TSDM snapshot information) is transferred using the VM Direct Engine VMware APIs.
Note: From this point in time, the files on the PowerProtect appliance are crash consistent and can be used for recovery. For a full backup, both full sync and delta sync are performed. However, for an incremental backup, only delta sync is performed. A full sync can back up four VM disks in parallel; a delta sync can back up 10 VM disks in parallel.
Figure 12. Delta sync operation