Backing up VMs: Agentless or Guest-Level Backup?
“Back up VMware” (or “back up Hyper-V) sounds straightforward enough. But of course, there’s more than one way to go about it (isn’t there always?). One term you’ll hear connected with VM backup (and VMware in particular) is “agentless” backup. What does this mean, and what’s the difference from VM backup that’s NOT agentless?
Virtualization 101: The Short Version
First, let’s take a step back. Most of you reading this are probably very familiar with how virtualization works, but if you’re new to the field, here’s a brief rundown.
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At its heart, virtualization is about making better use of resources. As VMware itself puts it, “Virtualization uses software to simulate the existence of hardware and create a virtual computer system. Doing this allows businesses to run more than one virtual system – and multiple operating systems and applications — on a single server.”
Resources like CPU (not to mention power, cooling and other physical considerations) are expensive, and a single system usually doesn’t use a server’s full capacity. By allowing multiple systems to take advantage of physical server resources, IT departments can reduce the number of physical servers they need (and thus reduce costs as well). The virtual servers are often called guest machines.
Just like physical servers, of course, virtual servers need to be backed up – which bring us to our main point. There’s two main ways to go about VM backup: in the guest machines, or in the hypervisor.
Agentless VM Backup vs. Guest-level VM Backup
Let’s start with guest-level backup (also called agent-based backup). This approach is very similar to backing up a physical machine: the backup software agent is installed on each guest as if it were an individual physical server. The software agent then works normally, making its configured backups of the guest machine.
The problem with guest-level VM backup is scale. If you only have a few virtual servers, it’s probably not a big deal to individually install and manage a software agent on each one. But if you’re one of those companies with hundreds (or thousands) of VMs, it’s a non-starter.
This brings us to agentless VM backup. Instead of installing a software agent on each guest, software is installed once on the hypervisor (in VMware this is usually called a “virtual appliance”). From there, it can automatically detect VMs and back them up. This is a lot more manageable than guest-level backup if you have a large or frequently-changing number of VMs in your VMware system.
Both agentless and guest-level backup will give you data protection for VMs – one is just much easier to operate. So if you have an environment where guest-level would be impractical, make sure not to just ask a prospective vendor is they “do VMware.” Ask how.