Application-Consistent Backups

Application-consistent backups are used to back up entities with high or extremely high transaction loads. Good examples of such entities can be Microsoft SharePoint, Active Directory, MS SQL Server, or Oracle database solutions.

When such high-transactional solutions become subject to back up, the key point is the memory state and current transactions are stopped, flushed to disk, and only then are backed up.

If memory cannot be flushed to disk for some reason, backup may not be valid for restore or some important data may be missing.

Thus, an application-consistent backup is a backup that is equipped with tools to notify applications about coming backup operation and allow applications to achieve a quiescent and consistent state by flushing all operations to disk.

This chapter covers the following topics:

• Frameworks for Application-Consistent Backups
• Application-Consistent Hyper-V Backups
  • Available Hyper-V Checkpoint Types
  • Configure Hyper-V Application-Consistent Backups

Frameworks for Application-Consistent Backups

Volume Shadow Copy Service (VSS) is a framework designed primarily to solve the application-consistent problems for Windows operating systems. VSS is an infrastructure that provides backup applications with the feature of creating application-consistent backups.

When backup job is initiated, VSS works as follows:

1. Every running application that needs to flush its data kept in RAM to disk is notified by VSS.
2. Then a Copy-On-Write operation is performed on volume.
3. A volume snapshot is done and can be processed by a backup application.

Application-Consistent Hyper-V Backups

Application-consistent backups of virtual machines in a Hyper-V environment are based on interactive checkpoint type selection.

Available Hyper-V Checkpoint Types

Windows 10 Hyper-V includes two types of checkpoints:

• Standard Checkpoints. A standard checkpoint takes a snapshot of the virtual machine and virtual machine memory state at the time the checkpoint is initiated. A snapshot is not a full backup and can cause data consistency issues with systems that replicate data between different nodes such as Active Directory. Hyper-V only offered standard checkpoints (formerly called snapshots) prior to Windows 10
• Production Checkpoints. Production checkpoint uses Volume Shadow Copy Service or File System Freeze on a Linux virtual machine to create a data-consistent backup of the virtual machine. No snapshot of the virtual machine memory state is taken.

Checkpoint Backup

Checkpoint creation logic in CloudBerry Backup depends on Hyper-V configuration. The following cases are possible:

• Production checkpoints are selected
• Standard checkpoints are selected
• Checkpoints are disabled (no checkpoint type selected)

Backup for Windows always starts by trying to create a checkpoint of the selected type first. In the event of a failure, a recovery inconsistent checkpoint will be created. The recovery inconsistent checkpoint does not contain the VM VSS snapshot. If no checkpoint type is set, MSP360 (CloudBerry) Backup starts by trying to create a recovery consistent checkpoint using VM VSS snapshot. In the event of a failure, a recovery inconsistent checkpoint will be created. The recovery inconsistent checkpoint does not contain the VM VSS snapshot. In case of recovery consistent checkpoint usage, I/O activities that are quiesced at a point of creating VM VSS snapshot will be resumed to ensure successful restore. In case of the recovery inconsistent checkpoint is used for restore, the restore may fail.

Configure Hyper-V Application-Consistent Backups

You can configure the application-consistent options on the Application Processing Options step of the VMware backup wizard. These options can be configured separately for each virtual machine.

Click the application processing value to change it, if necessary.

By default, the Try application processing setting is set. You can change these options separately for each virtual machine, if necessary.

The following options are available:

• Try application processing. Back up virtual machines 'as is' if failed. Once this option is selected, virtual machines are backed up one by one. The state of applications running on virtual machines is checked, then a recovery consistent checkpoint is made and an application-consistent backup is performed. In case an recovery consistent checkpoint cannot be not made for some reason, this virtual machine will be backed up 'as is'.
• Require successful application processing. Skip virtual machines if failed. Once this option is selected, virtual machines with applications that did not flush pending I/O operations from memory to disks, are skipped and an appropriate warning is displayed for a user.
• Disable application processing. Back up virtual machines 'as is'. Once this option is selected, regular VM snapshots are done without quiescing.