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In many cases, changes to a VM's disk should survive a shutdown an be present when it is launched again. In some cases, you want an unchanged copy of a disk for each instantiation of the template. This behavior is controlled by a property called persistent with values yes or no.
When you import an appliance from the AppMarket, the disk image(s) normally have persistent=no.
This means, in short, that changes are lost.
At each instantiation of the template, a copy of the image is made and attached as a disk to the VM. Any changes to the VM's disk are discarded when terminating the VM.
If you want to run multiple VMs with a disk from the same image, you need persistent=no, because one disk image cannot be connected to more than one VM. Compare this to a real hard drive that can only be connected to one PC at a time. Persistent=no creates a copy for each VM. This implies that changes to the disk are not shared with or propagated to the other VMs.
You can change the persistent property by selecting a disk and using the pencil icon to the right of the property
or the drop down menu to the right of the clone button.
If you have a non-persistent disk, but found that you have made changes you do want to keep, please refer to the page about storage snapshots.
A disk image with persistent=yes will keep its changes after shutdown of the VM.
Persistent=yes implies that you cannot connect this disk image to more than one VM at the same time.
Compare this to a real hard drive that can only be connected to one PC at a time.
It is possible to have the image in more than one template, as long as at most one template is instantiated.
This can be useful when a template with 32 cores needs a software update: use a similar template with only one core.
You can change the persistent property by selecting a disk and using the pencil icon to the right of the property
or the drop down menu to the right of the clone button.
