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Agent vs. agentless backup: Which is the best option?

In the debate between agent-based and agentless backups, agentless tends to win out. However, factors such as environment and hypervisor capabilities can impact that decision.

In the current world of data protection, agent vs. agentless backup seems like a simple choice. Where possible and affordable, it makes sense to use agentless backup. However, sometimes that is simply not an option.

Numerous factors contribute to the choice between agent-based and agentless backup. The age of the system being managed, existing backup infrastructure and the limits of what the current backup software can achieve all affect the feasibility of using agentless backups.

It is key to understand where both agent-based and agentless fit into the data backup equation. In addition to comparing agent vs. agentless backups, we will also discuss the choice between image-based vs. file-based backups.

What are agent-based backups?

Agent-based backups refer to a backup mode when a server uses backup agent software perform the backups. Organizations still use agent-based backups in modern environments, partly due to their use of backup agents in legacy systems.

Agent-based backups use a classic client-server model where the server pulls all the backups at a file level. At the end of the day, agents are essentially applications that organizations install on the server to be backed up.

As systems scale up, the management of backups becomes more complex. The compute resources required to perform agent-based backups can eventually slow performance and impact workloads. Agent-based backups are typically used with physical environments since virtual environments scale up much faster and individual backup agents become difficult to manage.

What about agentless backups?

Agentless backup does not require users to install software on individual servers, instead using disk-to-disk backup from a centralized point.

Agentless backups are the de facto standard in the world of virtual machines.

In the agent vs. agentless backup debate today, agentless backup is often the preferred option, especially for virtual environments. Agentless backups require fewer resources because organizations don't have to install an agent on each server, causing a lot of resource and management overhead.

Modern hypervisor and cloud-based infrastructure lend themselves much more readily to agentless backups, which are often easier to manage on a day-to-day basis. However, the capabilities of the hypervisor in use makes or breaks the possibility of agentless backup. Most modern mainstream hypervisors do support agentless backups, but users should check the documentation to verify this.

Image-based vs. file-based backups

Image-based backups refer to a situation where a crash-consistent point-in-time snapshot of the entire server is taken as a backup and can be restored if needed with minimal management overhead. The alternative to this is file-based backups, where each file is backed up individually.

Image-based snapshots tend to be more useful because it provides a consistent point-in-time copy of the server at the block level. No longer does the administrator get a warning about certain files not being backed up because they are locked open and, therefore, not backed up. The image snapshot happens at the lowest level and looks at block-level changes, not files.

Image-based snapshots go hand in hand with agentless backups. Agentless backups are the de facto standard in the world of virtual machines. Rather than having to install an agent on each individual server, the hypervisor usually exposes API endpoints for these agentless backups and does the bidding on their behalf.

Instead of having an agent installed on every VM, consuming space, memory and CPU resources, the agentless backup system requests a snapshot of the VM to be backed up. There are no individual agents to maintain, just the backup software.

Stuart Burns is a virtualization expert at a Fortune 500 company. He specializes in VMware and system integration with additional expertise in disaster recovery and systems management. Burns received vExpert status in 2015.

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