Virtualization Overview

Virtual Environment Protection Overview

Virtualization has become the standard of data center consolidation whether on-premise or in the cloud. As the number of virtual machines and the physical hosts they run on grows, a comprehensive protection strategy is required to ensure proper protection. Commvault^® software provides several protection methods for virtual environments on premise and in the cloud. These methods provide a comprehensive enterprise hybrid protection strategy.

There are four primary methods Commvault^® software can use to protect virtual environments:

• Virtual Server Agent (VSA)
• Application Aware backup integrating the VSA and application plugins
• Agents installed within virtual machines
• IntelliSnap^® Technology

Which method is best to use depends on the virtual infrastructure, type of virtual machines being protected, and the data contained within the virtual machines. In most cases using the Virtual Server Agent (VSA) is the preferred protection method. For specific virtual machines, using 'application aware' backups or an agent directly installed within the VMs is the preferred method. For mission critical virtual machines, large virtual machines or virtual machines with high I/O processes, the IntelliSnap feature is used to coordinate hypervisor software snapshots with array hardware snapshots to efficiently protect virtual machines while minimizing the performance impact of the virtual infrastructure.

Virtual Server Agent (VSA)

The Commvault Virtual Server Agent (VSA) interacts with the hosting hypervisor to provide protection at the virtual machine level. This means agents do not need to be installed directly on the virtual machines, although installing restore-only agents provides a simplified method for restoring data back to the VM.

Depending on the hypervisor application being used and the virtual machine's operating system, different features and capabilities are available. The VSA interfaces with the hypervisor's APIs and provides capabilities inherent to the application. As hypervisor capabilities improve, the Commvault VSA agent is enhanced to take advantage of new capabilities.

Agent-Based Protection

Agent-based protection uses Commvault agents installed directly in the virtual machine. When an agent is installed in the VM, it appears in the CommCell^® console just like a regular client and the functionality is the same as an agent installed on a physical host.

The main advantage with this configuration is that all the features available with Commvault agents are used to protect data on the VM. For applications, using a Commvault agent provides complete application awareness of all data protection operations including streaming log backups, granular item-based protection, archiving and content indexing.

VSA Application Aware Protection

VSA application aware backups insert an 'application plugin' into the VM during a VSA backup. When a VM backup runs, the plugin quiesces the application using a VSS snapshot. The VSA coordinator then communicates with the hypervisor to conduct a VM snapshot. This protection method provides a hybrid approach using the VSA to conduct data protection jobs, and agent-based functionality for recovery, similar to installing an agent directly in the VM.

IntelliSnap^® for VSA

The Commvault IntelliSnap^® feature provides integration with supported hardware vendors to conduct, manage, and create backup copies of snapshots. This technology is used to snap VMs at the Datastore level and back them up to protected storage.

The process for protecting virtual machines is similar to performing snapshots with the VSA agent directly interfacing with the hosting hypervisor application. The VSA first quiesces the virtual machine and then the IntelliSnap feature uses vendor API's to perform a hardware snapshot of the Datastore. The Datastore is then mounted on an ESX proxy and all VMs are registered. Finally, the VMs are backed up and indexes are generated for granular level recovery. The snapshots can also be maintained for live browse and recovery. The backup copies are used for longer term retention and granular browse and recovery.

Virtualization protection methods high level concept

Protecting Virtualized Applications

Commvault^® software provides several methods for protecting virtualized applications:

• VSA Application consistent backups using Volume Shadow Services (VSS) to quiesce application data
• VSA Application aware using agent plugins to quiesce application data
• Agents deployed within the virtual machine
• IntelliSnap for VSA using the VSA Application aware settings or agents installed in the VM
• Freeze / thaw scripts

Each one of these methods have specific advantages. To determine which option is best, details about the application need to be known:

• Business importance of the application
• Normal I/O of data within the virtual disks during backup windows
• Size of application data requiring protection
• Does the application data reside within virtual disks or on RDM volumes?

Application and Crash Consistency

Before determining which Commvault option is best to protect application data, an understanding of Crash Consistency and Application Consistency is required. The consistent state of application data is essential to provide a backup which can be restored in a proper state. Many applications do have a built-in reconciliation process that can return application data to a consistent state. It's important to note that this process could take a long time and application experts may be required to assist in the process. Using Commvault features to ensure a consistent state makes restore operations faster and simpler.

Crash Consistent

Crash Consistent backups are based on point-in-time software snapshots and backup operations of a virtual machine that allows the VM to be restored to the point in which it was snapped. When the snapshot occurs, all blocks on the virtual disks are frozen for a consistent point-in-time view. The application is not aware that this process is occurring.

There are several issues when performing crash consistent snapshot and backup operations. The first issue is that if an application is running on the virtual machine, it is not aware the snapshot is being taken. VSA communicates with the hosting hypervisor to initiate snapshots at the VM level and there is no communication with the application. Any I/O processes being conducted by the application will continue without any knowledge that the snap has been performed. This can cause issues during restore operations as the application data will be restored to the exact point where the software snapshot was conducted.

Example: a database application is conducting a maintenance to defrag and reorganize data within its files. In the middle of this process, the software snapshot occurs. When the VM is restored, it will be placed in the state of the maintenance period.
Another issue in this case would be larger than normal snapshots as all the block changes are cached to keep the production virtual disk in a consistent state. This will cause a longer than normal cleanup process when the snapshot is released and may cause storage space issues on the production volume.

Crash consistent snapshot

Application Consistent

With Application Consistent protection, the application itself is aware that it is being snapped. This awareness allows for the data to be protected and restored in a consistent and usable state. Application aware protection works by communicating with the application to quiesce data or by using scripts to properly quiesce the data. Application consistent protection is not critical for file data but is critical for application databases.

There are several methods to provide application consistent protection:

• Commvault agents
• Application Aware VSA Backup
• Application Consistent VSA Backup
• Scripting Database Shutdowns

Commvault® Agents

An agent installed in the VM will directly communicate with the application running in the VM. The agent communicates with the application to properly quiesce databases. A streaming backup of application data is then conducted. If the application data is on an RDM volume, the application agent can be used with the IntelliSnap feature to quiesce the data and snap the volume. A proxy host can be used to back up the data avoiding load on the VM or hypervisor. Using application agents in the VM also provide database and log backup operations and a simplified restore method using the standard browse and recovery options in the CommCell^® console. Commvault agents in the hosting VM are recommended for mission-critical high I/O applications.

Application Aware VSA backup

An application plugin is pushed to the VM to properly quiesce application data. The plugin communicates directly with the application and the VSA to ensure a proper quiesce of application data. The quiesce process uses VSS to quiesce the data and is supported on Windows-based VSS aware application including SQL, Exchange, SharePoint and Oracle on Windows. It is important to note there are certain limitations for Exchange DAG and SQL always on configurations. Check with the Commvault Online Documentation for the latest support and enhancements for Application Aware VSA backup.

This protection method is recommended on low to medium I/O applications.

Application Consistent VSA backup

The Volume Shadow Services (VSS) is used to quiesce application data. This method works for Windows-based application that are VSS aware including SQL, Exchange and Oracle on Windows. When the VSS call is made to the VM, any VSS aware applications attempt to quiesce. If the attempt is successful, the backup is application consistent. However, if the VSS quiesce fails, which can occur if there is too much application I/O at the time of the quiesce, the backup will only be crash consistent. This method is not recommended for high I/O virtual applications.

Scripting Database Shutdowns

Using external scripts which can be inserted in the Pre/Post processes of a subclient, or executed as part of a Workflow, application data can be placed in an offline state to allow for a consistent point-in-time snap and backup operation. This requires the application to remain in the offline state for the entire time of the snapshot operation. When the VM is recovered, the application must be restarted after the restore operation completes. This method is only recommended when Commvault agents are not available for the application.

Impact on Software Snapshots and Volumes During VM Backups

It is important to note that even with an application consistent backup, problems can still occur. For high I/O applications running in virtual machines, software snapshots managed by the hypervisor can grow beyond a manageable level. This can result in running out of disk space on the volume or a failure to clean up software snapshots.