Agentless Backups: Best Practices



What are the best practices to ensure Agentless backups run without any issues?


  • Agentless backups


Common causes of issues on Agentless backups

Changing virtual Disk sizes

Check that the volume’s virtual disk size is set to a whole number. Any storage set to a fraction of a GB throws a fractional size error, which can result in the Invalid Root File System message. 

If the Virtual Disk Size is listed in TB, you can use the dropdown to view the value in GB, but do not press ok or apply.

If the volume is set to a fraction, round the space up to the next GB.In the image above, you'd change the storage to 36 GB. 

Address any "Disk needs consolidation" messages as necessary

If you see a "Disk needs consolidation" message, consult this article.

Disabling Snapshots

Snapshots are useful as a secondary backup method for short-term or ad-hoc backups. Keeping snapshots for a long period of time will negatively impact the performance of your production VMs. Finally, consolidating a virtual disk that has long-term snapshots takes a very long time, and can cause a negative impact on the I/O performance of that VM.

By default, the snapshots taken by Datto appliances persist for only as long as it takes to back up any given target virtual machine.


Verifying quiescing is enabled

The Datto solution leverages a VMware feature called quiesced snapshots. When taking a quiesced snapshot, VMware pauses writes to the virtual machine's virtual disk to achieve a consistent state. To back up a Windows guest OS, the Datto solution also uses the virtual production machine's VSS writers. If a quiesced snapshot of a VM fails to complete, a backup job will not run. Without quiescing, VMware snapshots are only crash-consistent.

Changing VM Templates
CBT (Changed block tracking) needs to be enabled for incremental agentless backups to function, that requires a VM template of at least version 7.

Additional resources

Was this article helpful?

0 out of 0 found this helpful

You must sign in before voting on this article.

Calling all Partners! We want to hear your feedback! Please participate in this quick survey and help us build a better, more-relevant Knowledge Base!

Want to talk about it? Head on over to our Community Forum!