Backup

Bacula Enterprise Only

This solution is only available for Bacula Enterprise. For subscription inquiries, please reach out to sales@baculasystems.com.

The backup of a single guest VM takes the following steps:

Export guest VM metadata configuration for future restore.
Backup OS disk.
Backup all data disks
Wait for all procedures to finish
Add new snapshot to a tracker and check for older snapshot to delete

Disk backup procedure

The same process is used to backup OS or data disk, it follows the following steps:

Create a snapshot of the disk
Issue an SAS token on the snapshot just created.
Move snapshot data to a blob
Revoke SAS token
Stream disk data or incremental changes to Bacula

Bacula Files

The backup will create the following backup files for each guest VM:

A single empty file to match a guest VM name to its UUID /@azure-vm/<vmUuid>_<vmName>.name
A single configuration metadata file: /@azure-vm/<vmUuid>/<epoch>_conf
A unique raw data file for the guest VM OS disk /@azure-vm/<vmUuid>/<epoch>_osdisk
A raw data file for each data disk: /@azure-vm/<vmUuid>/<epoch>_<index>

At restore time the user can identify the guest VM using the UUID to mark the corresponding files:

+-------------------------------------------------------------------+
| filename                                                          |
+-------------------------------------------------------------------+
| /@azure-vm/690d74f9-9ce4-45fb-9b23-149afebe18f7_VmName.name       |
| /@azure-vm/690d74f9-9ce4-45fb-9b23-149afebe18f7/1661160371_conf   |
| /@azure-vm/690d74f9-9ce4-45fb-9b23-149afebe18f7/1661161330_0      |
| /@azure-vm/690d74f9-9ce4-45fb-9b23-149afebe18f7/1661167810_osdisk |
+-------------------------------------------------------------------+

Incremental Backup Fallback Process

During incremental backup if the plugin fails for any reason to compute incremental changes for a disk the disk will be backed up as a full image instead. A message will be displayed and the resulting backup will end with a Backup OK with warning status. At restore time the user must carefully mark the files for restore by ignoring older full/incremental images of said disk.

Snapshot Safekeeping and Data Usage

Microsoft Azure uses a disk by disk snapshot policy. Bacula will keep track of snapshot relation between one another and delete snapshots that are no longer relevant. However, multiple snapshots of the same disk can be expected on the storage at any given time.

On Microsoft Azure incremental snapshots appear to have the same size as the full disk. However, the data contained inside the snapshot will be the differential data. Per Azure documentation incremental snapshots are billed for the used size only.