On 10/13/2015 09:59 PM, Eric Blake wrote:
On 10/13/2015 09:46 PM, Nathan Shearer wrote:
I have a script that performs a backup with the following steps:
virsh dumpxml --inactive "$DOMAIN" > "$TMP/${DOMAIN}.xml" && \ virsh dumpxml --inactive "$DOMAIN" > "$DESTINATION_XML" && \ virsh undefine "$DOMAIN" && \ virsh blockcopy "$DOMAIN" "$SOURCE_DISK" "$DESTINATION_DISK" --wait --verbose --finish && \ virsh define "$TMP/${DOMAIN}.xml"
It's basic and did work for creating basic backups. Is there a way to do this without undefining the domain? Not yet. Qemu doesn't yet support persistent bitmaps; there is upstream work trying to add it, which might make qemu 2.5, and then libvirt has to be taught to use it.
I recently had to redefine the VM from a backup XML because this script failed during the block copy step. Why can't I blockcopy a domain that is defined? Why does it need to be undefined first?
Without a persistent bitmap, libvirt cannot restart a copy operation efficiently. Requiring the domain to be transient (via the undefine/define wrapper around the blockcopy) was a design decision made when blockcopy was first added to make the caller aware of the limitations, and put the caller in charge of what happens if the domain disappears in the middle of the operation. We hope to lift that limitation when support for persistent bitmaps lands.
Okay, I'll just make my script a little more intelligent while I wait for the newer versions. Definitely looking forward to qemu 2.5 and an updated libvirt :)