Virtual machine backup strategies for optimal business continuity

Jayant Walvekar and Pankaj Khandelwal

IT Managers certainly have an unenviable job. Not only do they have to guard fiercely their company's data against hackers and phishers, but also ensure its safe journey to virtual servers. And virtual server backup brings in several issues, especially due to virtual server sprawl. Besides the security risks, it also requires tremendous resources to perform server backups and ready them for recovery in case of a disaster.

In a typical

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virtual server environment, there are three possibilities when taking backups:

- Backup of files on a virtual machine (VM).
- Backup of a VM.
- Backup of a hypervisor console. For example, backup of the VMware ESX console OS.

Traditional backups copy programs and application data, but do not necessarily capture the entire VM state. To counter this problem, VM Snapshot can be used to backup the entire machine state.

The usual backup methods can cause many server environments to limit the number of VMs they place on a single ESX server, decreasing the overall value proposition of server virtualization. An off-host backup facilitated by native tools such as VMware Consolidated Backup (VCB) on VMware ESX is an effective technique to minimize the backup process' impact on a virtualized server. In this technique, a proxy server is used to take the backup, which directly works with a VM snapshot or virtual disks. The physical server or VM needn't participate in actual data transfer, thus minimizing resource requirements. Moreover, most of the leading third party backup software solutions integrate with VCB to offer off-host backup features.

There are multiple ways in which virtualized servers are protected:

Snapshot VM: This process is typically used to backup a VM. To ensure consistency at the application level, it requires third party software such as integration with the Volume Snapshot Service (VSS) on Windows.
Backup by installing agents inside a virtual machine: Typically used to take file backup. This technique however, consumes VM and server resources.
Off-host backup using a third-party backup software or VCB: This technique can be used to achieve all three possible backup methods listed above, and ensures least impact on server or workload performance

There are various parameters to evaluate backup need of VMs like:

1) Nature of workload on VM.
2) Criticality of workload. For example, uptime requirements.
3) Rate of data change of workload. For instance, an Oracle database workload will have higher rates of data change, than say a web server workload.
4) Required or available backup window(s).

Another issue which organizations often face with VM backup, is that traditional backups copy programs and application data, but do not necessarily capture the entire virtual machine state. To counter this problem, VM Snapshot is a methodology by which one can backup entire machine state. However, snapshots require third party software (such as those that integrate with VSS on Windows) for VMs to be in transaction-consistent state and useable when needed.

Here are a few tips to help improve backups of virtual servers:

- Consider all the backup requirements especially RPO and RTO at the time of planning and design.
- Consider different backup methods and strategies to choose ones that meet the requirement.
- Use disk-based backups, at least for staging.
- Use data reduction techniques to optimize the amount of data.
- Use Backup software that integrates well with native backup tools such as VCB. - Use image reduction techniques offered by virtualization vendor or third party.

About the author: Jayant Walvekar is the associate vice president for virtualization and storage at Persistent Systems. Pankaj Khandelwal is the consultant for virtualization and storage domain at Persistent Systems.

(As told to Jasmine Desai.)


This was first published in October 2009

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