Source
-------

$> ls -lash src-disk.qcow2 
15M -rw-rw-r--. 1 kashyapc kashyapc 15M Nov 14 16:31 src-disk.qcow2

$> ~/build/qemu-build/x86_64-softmmu/qemu-system-x86_64 -display none -nodefconfig -nodefaults -m 512 -device virtio-scsi-pci,id=scsi -device virtio-serial-pci -drive file=./src-disk.qcow2,f
ormat=qcow2,if=virtio -serial unix:/tmp/monitor,server,nowait -qmp stdio
{"QMP": {"version": {"qemu": {"micro": 90, "minor": 10, "major": 2}, "package": " (v2.11.0-rc0-47-g55ed8d6)"}, "capabilities": []}}
{ "execute": "qmp_capabilities" }
{"return": {}}
{"execute":"migrate-set-capabilities","arguments":{"capabilities":[{"capability":"pause-before-switchover","state":true}]}
}
{"return": {}}
{ "execute": "drive-mirror", "arguments": { "device": "virtio0", "target": "nbd:localhost:3333:exportname=virtio0", "sync": "full","format": "raw", "mode": "existing" } }
{"return": {}}
{"timestamp": {"seconds": 1510674730, "microseconds": 406831}, "event": "BLOCK_JOB_ERROR", "data": {"device": "virtio0", "operation": "write", "action": "report"}}
{"timestamp": {"seconds": 1510674730, "microseconds": 407580}, "event": "BLOCK_JOB_ERROR", "data": {"device": "virtio0", "operation": "write", "action": "report"}}
{"timestamp": {"seconds": 1510674730, "microseconds": 408316}, "event": "BLOCK_JOB_ERROR", "data": {"device": "virtio0", "operation": "write", "action": "report"}}
{"timestamp": {"seconds": 1510674730, "microseconds": 409016}, "event": "BLOCK_JOB_ERROR", "data": {"device": "virtio0", "operation": "write", "action": "report"}}
{"timestamp": {"seconds": 1510674730, "microseconds": 409099}, "event": "BLOCK_JOB_ERROR", "data": {"device": "virtio0", "operation": "write", "action": "report"}}
{"timestamp": {"seconds": 1510674730, "microseconds": 409168}, "event": "BLOCK_JOB_ERROR", "data": {"device": "virtio0", "operation": "write", "action": "report"}}
{"timestamp": {"seconds": 1510674730, "microseconds": 575266}, "event": "BLOCK_JOB_COMPLETED", "data": {"device": "virtio0", "len": 41156608, "offset": 16777216, "speed": 0, "type": "mirror", "error": "Input/output error"}}


Destination
-----------

$> qemu-img create -f qcow2 -o preallocation=falloc dest-disk.qcow2 16M

$> ~/build/qemu-build/x86_64-softmmu/qemu-system-x86_64 -display none -nodefconfig -nodefaults -m 512 -device virtio-scsi-pci,id=scsi -device virtio-serial-pci -drive file=./dst-disk.qcow2,format=qcow2,if=virtio -serial unix:/tmp/monitor,server,nowait -incoming tcp:localhost:6666 -qmp stdio
{"QMP": {"version": {"qemu": {"micro": 90, "minor": 10, "major": 2}, "package": " (v2.11.0-rc0-47-g55ed8d6)"}, "capabilities": []}}
{ "execute": "qmp_capabilities" }
{"return": {}}
{ "execute": "nbd-server-start", "arguments": { "addr": { "type": "inet","data": { "host": "localhost", "port": "3333" } } } }
{"return": {}}
{ "execute": "nbd-server-add", "arguments": { "device": "virtio0","writable": true } }
{"return": {}}


$> ls -lash *
17M -rw-r--r--. 1 kashyapc kashyapc 17M Nov 14 16:52 dst-disk.qcow2
15M -rw-rw-r--. 1 kashyapc kashyapc 15M Nov 14 16:31 src-disk.qcow2