Step 4: Select the Backup Approach for Each Application

Article
02/25/2008

Published: November 12, 2007 | Updated: February 25, 2008

The backup approach selected for the virtualized applications affects the storage and network infrastructure of the host system. Several approaches are available for meeting applications’ backup and restore requirements.

There are three basic options for performing backups for the applications identified in step 4. In this step, each application is reviewed to determine which backup approach to use. The decision should be recorded in the job aid chart.

Option 1: Per Application

Products such as SQL Server and Exchange Server have specific backup application requirements to ensure that a complete backup is obtained. That is, ensure that not only the data files are backed up but also that transactions in memory and transaction log files are committed to the database.

Performing application-level backups has several useful benefits. First, the backup-related functionality is typically designed specifically for protecting an application. It helps ensure that files that are typically in use are backed up in a consistent state. Additionally, the restore process is often simplified because administrators can use application-level features to bring data back online. The backup files themselves can be significantly smaller than those generated from a guest- or host-level backup.

Application-specific backups can have a significant impact on the host system from a CPU, disk, and network usage perspective.

Option 2: By Guest

In guest-level backups, VMs essentially function the same as physical machines. Each computer may include a backup agent responsible for transferring backups to a designated storage location, or they can use the native Windows Backup application. Guest-based backups can have a significant impact on the host system from a CPU, disk, and network usage perspective.

Option 3: By Host

When performing backups at the host level, two options are available with Virtual Server 2005 R2 SP1:

Offline backups. This approach requires turning off the VM or placing it in a saved state before copying files. After the copy process is complete, the VM can be started again. This approach involves downtime for each VM, but it provides a simple method for implementing complete backups.
Online backups. Using snapshot technology such as Volume Shadow Copy Service (VSS), administrators can make copies of VM configuration files while the VM is running. Doing so avoids downtime but may affect performance momentarily. This option is only available on hosts using Storage Area Networks (SANs) that have a VSS writer available.

The reason for understanding the type of backup approach for each application is to:

Allow for the possibility of grouping VMs with similar backup requirements onto the same hosts (for example, all VMs using host backup are placed on the same host).
Determine the impact that backups will have on the host system from a CPU, network, and disk usage perspective.

Evaluating the Characteristics

Additional characteristics to consider include are discussed in the following tables.

Complexity	Justification
Per application	Different backup methods must be used for different applications.	H
By guest	Backup options can be centrally managed using enterprise backup software.	M
By host	Requires no knowledge of the VM’s contents; therefore, backups can be performed consistently across the entire environment.	M

Performance	Justification
Per application	Backups include only important data.	↓
By guest	Backups are treated the same as physical machines and can include the operating system, program files, and user data.	↓
By host	Backups include the entire contents of a VM, usually requiring more time and storage space. However, backups can be performed while the VM is turned on.	→

Validating with the Business

Technical requirements often drive decisions about specific backup approaches. However, be sure to ask the following questions to ensure that business needs are met:

Is it necessary to back up all the content for a specific workload or application? In some cases, application experts might determine that it is necessary to store only certain information in backup files because users can easily re-create other data in the event of a failure.
Will the determined approach meet data loss requirements? Perform backups frequently enough to ensure that data loss is minimized for critical applications.
Does the recommended approach meet recovery requirements? Business users will likely have expectations related to the amount of time required to recover from various failure scenarios.

Based on answers to these questions, backup-related decisions for specific applications may need to be reviewed and revised.

Decision Summary

At the end of this step, sufficient information about the expected backup approach for each application that will move to a virtual infrastructure should be available. In some cases, it may be desirable to note which backup strategies are possible and which are preferred based on the needs of the VM.

Additional Reading

The Windows Server TechCenter article, “Backing up and restoring Virtual Server,” at https://www.microsoft.com/technet/prodtechnol/virtualserver/2005/proddocs/vs_operate_using_backUp.mspx?mfr=true addresses considerations for implementing Virtual Server 2005 backups.

This accelerator is part of a larger series of tools and guidance from Solution Accelerators.