Backup Restore

Agent-based VMware Backups

My last blog post contained a poll asking visitors about their primary VMware backup methodology.  The survey listed the common approaches to protecting virtualized environments including traditional agent-based,  VCB/VADP, dedicated VMware backup application, snapshots and doing nothing.  The results suggest that that the agent-based approach is most commonly used.  I anticipate that end users will migrate to backup methodologies that support VMware’s VADP functionality, but believe that there will always be a subset of people who rely on the agent-based approach. When implementing the agent-based approach, you should consider the following:

Benefits of Agent-Based Backup Models:

Transparent to existing processes – The agent-based approach is exactly the same as the traditional physical server model and so most backup administrators are familiar with the process.  With this approach, each VM has a separate client backup license and transfers its to the backup server over the LAN.

Granular restores – Each VM is backed up at the file level.  Therefore, standard incremental and/or full backup policies apply and file-level recoveries are possible regardless of OS.

Application consistency – Backup vendors provide a variety of server agents that ensure that specific applications (like Exchange, SQL or Oracle) are quiesced prior to backup.  These same agents can be used inside the VMs to ensure that running applications are in a consistent state during backup.  A consistent backup ensures the fastest and most reliable recoveries.

Challenges of Agent-Based Backup Models:

System resources – The process of backing up a VM can be I/O and CPU intensive – a situation that is exacerbated by backing up multiple VMs on the same host simultaneously.  The agent-based approach creates the challenge of managing the backup process to minimize simultaneous VM backups.  The proliferation of VMs can make this process highly complex.

Software licenses – This approach requires a client license for every VM that is protected plus the end user must purchase and install new client licenses every time a new VM is provisioned.  The management of client licenses can rapidly become challenging.

Bare metal recovery – One of the benefits of VMware is the ability to duplicate VMDK files easily to allow for the rapid creation of new VMs.  Ideally, a VMware backup would enable this functionality by providing an image-based backup and recovery feature.  Unfortunately, the traditional agent-based model does not meet this requirement.  Agent backups are file-based and so the only recovery possible is at the file level.  If a VM fails and must be recovered, then the traditional restore process of installing the OS, then the desired application and finally recovering the data will apply.

It is clear that there are benefits and challenges to the agent-based backup approach.  This model is very familiar to most backup administrators since it is nearly identical to a physical server backup process.  The approach ignores some of the advanced features in VMware such as the VMware API for Data Protection (VADP).  However, the mature application support of the agent-based model still makes it appropriate for some data types, and will maintain its relevance long into the future.

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