Quote:
Originally Posted by shengyang999
Hi all,
i am newbie on KVM and have some questions regarding to the snapshot and backup.
First I want to know that what's the difference between snapshot and backup since the snapshot image can also be used as the backup image, right?
thanks for your reply
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No, in KVM snapshots work a little different then in other hyper visors.
When you snap an image in kvm all you are doing is creating a new writable image and leaving the original image read-only, KVM refers this as a "backing image"
If you only save the snap you only have the data from after you created the snap, no OS no nothing, just everything after the snap was created.
Now if you want to create a backup, you would create a snapshot, copy the backing image (the original image) to the backup location and then live merge the snapshot back into the backing image.
This ensures two things:
1) anything written to disk will not be copied while you are transferring your backup.
2) anything written to the snap will get merged back in to the original disk so those changes are not lost during the backup process.
This is en entirely live process, meaning the VM doesn't get interrupted at all while you are backing this image up.