Does Time Machine use a differential/delta file compression when copying files ?

FatMac\>MacPro wrote:

Csound1 wrote:

What do you categorize as a 'true' backup

The VM file or the Mac gets trashed and you need a copy of the VM from somewhere else. So you go to your backup.

Restore the snapshot.

We have VMs for a few of our users and the doc files for the VMs are saved/stored on the Mac OS profile. When Time machine runs a backup, the VM document files saved in the Host OS is backedup as well. Also, we keep a backup image of the VM in our network storage. So if something happens to the guest OS, we pull the VM image from the network storage, configure it, and assciate it with the documents backedup using TimeMachine. Not sure if that's what you're looking for.

Csound1 wrote:

FatMac\>MacPro wrote:

Csound1 wrote:

What do you categorize as a 'true' backup

The VM file or the Mac gets trashed and you need a copy of the VM from somewhere else. So you go to your backup.

Restore the snapshot.

At least in Fusion, the "snapshot" is a series of files included in what's normally considered to be the VM file, so if the VM file is trashed, the snapshot is too.

FatMac\>MacPro wrote:

Csound1 wrote:

FatMac\>MacPro wrote:

Csound1 wrote:

What do you categorize as a 'true' backup

The VM file or the Mac gets trashed and you need a copy of the VM from somewhere else. So you go to your backup.

Restore the snapshot.

At least in Fusion, the "snapshot" is a series of files included in what's normally considered to be the VM file, so if the VM file is trashed, the snapshot is too.

Yes, if the VM is lost the snapshot won't help. So exit the VM now and again and let TM back it up. Then use snapshots.

Csound1 wrote:

Yes, if the VM is lost the snapshot won't help. So exit the VM now and again and let TM back it up. Then use snapshots.

I've been curious about how TM treats VM's in flux (i.e., in use) because of the general agreement on the Fusion forum that VM's will be backed up by TM running automatically. Given their size and the time and space necessary for TM to capture them, I've been doing what Linc Davis advises, excluding them from TM and including them in full, bootable backups on external drives.

ohault wrote:

A) if files are locked, the backup should be configured to skip them.

Locking is a messy concept. Time Machine skips files that are currently in use. This prevents backing up a file that is in the process of being changed but it doesn't help the problems of backing up 28 GB when only 28 kb have really changed.

B) Many Virtual Machines (VM Ware Fusion, VirtualBox, ...) has built-in mechanism and APIs to create snaphots while the VM is running. In that case, Time Machine will not backup the running VMs but snapshots. Snapshoots are also big files.

Those Virtual Machines also have built-in mechanisms to keep themselves out of Time Machine. Have you tried turning that on and then turning on the snapshot functionality? Perhaps it will just do the right thing. If not, you can suggest that as an enhancement for the VM software.