Is virtual machine suspension enough before backup?

[cookieme]

I use Carbon Copy Cloner to make backups of my macOS Monterey Data volume to an external disk. With regards to the Fusion virtual machines, if they are powered off I know the backup will be fine as the vmdk files are not changing. However, sometimes I need to run a CCC backup task and I don't want to disrupt my work and power off the virtual machine(s).

What I'm wondering is if it's enough to have a pre-backup script that CCC runs that will suspend any running VMs and after CCC is done, the VMs will be powered back on. Will suspended VMs backup without any inconsistencies?

I've seen a member on here who has created a third-party tool for VM backups, but I'd like to leverage my existing backup solution if possible 🙂

Does the community have any DIY scripts to do this?

[wila]

Hi,

In theory yes.

Note however that your VM should be fully suspended before any file is copied via CCC.

In practice... I have not tested this and as such I highly recommend that you test it very carefully before using this in production. Not just making the backups, but also that you can actually resume your VM's.

Also note that a suspended on different hardware might not boot up anymore. Different hardware here also includes some macOS updates that change CPU and/or GPU flags on the same hardware.

If that happens you'll have to spend extra time discarding the suspend state and your VM will be of the "crash consistent" type instead of being able to resume.

--
Wil

[ColoradoMarmot]

So yes and no.  I've done this, with decent, but not 100% reliable results.  As Wil notes, you have to make sure that the VM is fully suspended - all memory dumped, and Fusion itself is quit before executing the CCC backup.  Otherwise when CCC does it's snapshot, it may snapshot an inconsistent virtual machine.  Note that this is *also* true if you have fusion configured to automatically reclaim disk space on shutdown of the guest, as that can take some time to complete.  On a fast SSD these are usually measured in seconds, but on a metal disk it could be minutes.

The other issue is if you try to resume the backup on a different version of Fusion, a different version of the OS, or a different machine. Any of those can cause issues.

So I guess the net is that yes, it works for quick and dirty backups, but if for anything that's mission critical, it's still best to shut down the VM before doing your clones.