Snapshots and Time Machine backups revisited

I'm still not clear how to backup VMs with Time Machine. On the Configuration Backup tab, if:

Time Machine: Do not backup virtual machine IS checked.
SmartGuard: Enabled IS checked.​

On the SmartGuard Details page:

Optimize for Time Machine IS checked​

Then if my Mac's disk has to be replaced, will I or will I not be able to restore the VM from Time Machine?

I've spent a lot of time reading KB and Forum articles about Snapshots and backing up with Time Machine but they're adding to the confusion. For example, KB8827 appears to start out saying Snapshots by themselves are sufficient with Time Machine. But then it closes with a section titled:

"If you do not want your virtual machine backed up by Time Machine:".​

Why would anyone want to backup the entire VM if Snapshots are sufficient? That sounds like Snapshots are NOT sufficient by themselves. Reinforcing that, the discussion of using SmartGuard in Forum article https://forum.parallels.com/threads/settings-for-time-machine-and-smart-guard.328818/ concludes with Dhruba@parallels agreeing with petri that:

Thank you very much. So am I right
- that I do NOT (my emphasis added) check the box 'Do not back up virtual machine' right above the enable box, and
- that I do not exclude the virtual machine in 'options' of Time Machine preferences?​

Which says it IS necessary to backup the entire VM in addition to keeping Snapshots. So if that's so, of what use are Snapshots? KB5691 lists the reasons why you might need snapshots but conspicuously does not include backups. That article sounds like Snapshots are more like Window's System Restore function; i.e., just intended to protect the OS but not all of the installed programs and user data. Is that correct?

I wish someone from Parallels who actually knows what's in Snapshots and understands how SmartGuard works would write a KB that explains how the "Time Machine" and" SmartGuard" options on the Configuration Backup tab are related and when you might want to use each of the four possible combinations of their states. And then please delete all the other articles about them or include a "superseded by" link to the new article to avoid future confusions. You might even revise the Help document to include this information.

 

I submitted the above post directly to Parallels via Help -> Request Support. The resulting dialog follows:
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From: Hemnath Prabagaran, Parallels
To: Stephen Van Dellen
Reply-To: pd-support@support.parallels.com
[Parallels #2170775] Questions Regarding Snapshots and Virtual Machine Backup
Hello Stephen,
Thank you for contacting Parallels Support.
From your e-mail, we understand that you have questions on backing up your Virtual Machine and taking snapsots.
When we take a snapshot, the entire data in the virtual hard disk drive [which is a part of the .pvm file (which again is your virtual machine)] until the point of time when the snapshot is taken, will be saved. Note that the afore-mentioned data includes the guest OS along all of its content (applications and personal and system files and folders).
When we take a backup of the .pvm file (which is your virtual machine), the whole content of the file bundle (of which the virtual hard disk drive is a part) is backed up.
We use snapshots to troubleshoot issues like data loss or data corruption within the operating system of the virtual machine. On the other hand, a backup of the .pvm file becomes useful when facing issues that affect more than just the guest OS, such as corruption of the entire virtual machine file bundle.
So in reality, if you are regularly backing up your virtual machine, you don't have to worry about keeping snapshots. Snapshots are sometimes preferred as they consume less space on your Mac hard drive compared to virtual machine backups.
Please let us know if you have any additional queries.
Thanks,
Hemnath Prabagaran
Customer Support
|| Parallels
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From: Stephen Van Dellen
To: pd-support@support.parallels.com
Re: [Parallels #2170775] Questions Regarding Snapshots and Virtual Machine Backup
Thanks for your quick response. So I think it says that if on the Configuration Backup page I:
- Check Time Machine: Do not back up virtual machine
- Check SmartGuard: Enabled
and on the SmartGuard Details page I:
- Check Optimize for Time Machine
then:
a) Time Machine will NOT include the entire VM in its backups.
b) If the disk has to be replaced, I'll be able to restore everything from Time Machine including the Snapshots but excluding the VM disk image.
c) I'll be able to restore the VM disk image from the Snapshots
Is that correct?
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From: Ajith Mamolin, Parallels
To: Stephen Van Dellen
Reply-To: pd-support@support.parallels.com
[Parallels #2170775] Questions Regarding Snapshots and Virtual Machine Backup
Hello Stephen,
Thank you for reply.
From your email, I understand you would like to know backing up your Virtual Machine with Time Machine.
I would like to inform you that snapshot is a saved state of a Virtual Hard disk you will not be able to recover the entire Virtual Machine using it. Also if your Mac hard disk is replaced you will not get your Virtual Machine back with snapshots. Please refer the articles given below to know more about snapshots and backup.
Working with snapshots - http://kb.parallels.com/5691
Backing up your virtual machine with Time Machine - http://kb.parallels.com/18827
Let us know if you have any additional queries.
We appreciate your time and consideration.
Thanks,
Ajith Mamolin
Customer Support
|| Parallels
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So it seems definite Snapshots do NOT include sufficient information to recover a VM if the hard disk fails. I guess I'll do the following unless someone has a better idea:
On the Configuration, Backup tab:
- Uncheck "Time Machine: Do not back up virtual machine" so Time Machine will include a copy of the VM in the next backup after any change to the VM's hard disk image.
- Uncheck "SmartGuard: Enabled". Since Snapshots include an image of memory and the processor's state, I see it's a good idea to take a Snapshot before you try something that may affect the Registry or other in-memory content before it's committed to disk. I don't see what good taking Snapshots routinely during normal operations is.
On the Options, Sharing tab:
- Set "Share Folders" to "Home folder only"
- Check "Shared Profile"
Since most routine Windows activities only affect the Home folders, I'm hoping having Windows share the Mac's Home folders will mean Time Machine only includes a copy of the VM's disk image when Windows is updated, programs are installed or removed or the Windows user changes their configuration options.