AlwaysOn Availability Groups allow you to increase fault tolerance between active and hot-standby databases without involving shared physical disks, which is quite important for virtualization of SQL Servers. Starting with version 8.0, Veeam Backup & Replication supports AlwaysOn Availability Groups for virtualized SQL Server 2012 and later.
Image-level Backup of SQL Server VM
During image-level backup of an SQL Server VM, Veeam requests and analyzes information about databases that are included in the AlwaysOn Availability Groups. Depending on the retrieved information, a VSS snapshot will be created with or without COPY_ONLY flag. The VSS_BS_COPY flag for VSS snapshot is triggered if the VM represents a secondary node for at least one AlwaysOn Availability Group (and this group is not in the Resolving state).
Veeam Backup & Replication also detects what cluster the database belongs to. If the backup job does not include all VMs from the cluster, a warning message will be issued.
Retrieved information is saved for further log identification.
Transaction Log Backup
Transaction log backup can be performed only for those databases that were successfully backed up with the corresponding settings, either on the primary or on the secondary node of AlwaysOn Availability Group.
Transaction logs processing interval may be the same, or may differ through the VMs included in AlwaysOn Availability Group –in the latter case, Veeam Backup & Replication will use minimal value (default is 15 min).
At each log processing interval, Veeam Backup & Replication chooses the AlwaysOn Availability Group node for which transaction logs will be backed up.
Logs are backed up for the only one AlwaysOn Availability Group node selected.
To become a subject for log backup, the node must meet the following criteria:
- Required Veeam components can be installed on that node (in particular, the VM must be running)
- If there are any logs remaining in the temporary folder on that node of AlwaysOn Availability Group, this means they were not backed up to the destination repository during the previous log backup session, so this node must be processed first.
- Databases in the AlwaysOn Availability Group(s) for that node were successfully backed up (for the last two processing intervals).
- Node should be available over the network (preferred data transfer method) or via VIX (for vSphere platform).
- The VM should be included in the list of preferred nodes (for backup) retrieved from SQL Server. If there are no preferred nodes, then any node can be chosen.