set cache for disk

templates/demovm.xml

@@ -34,7 +34,11 @@
   <devices>
     <emulator>/usr/bin/qemu-system-x86_64</emulator>
     <disk type='file' device='disk'>
-        <driver name='qemu' type='qcow2'/>
+        <driver cache="none" name="qemu" type="qcow2">
+          <metadata_cache>
+            <max_size unit='KiB'>{{ disk_cache }}</max_size>
+          </metadata_cache>
+        </driver>
         <source file='{{ disk }}'/>
         <target dev='sda' bus='sata'/>
     </disk>

vm.py

@@ -25,6 +25,7 @@ params = {
     "vgpu_type": "nvidia-1",
     "mdev_bus": "0000\:01\:00.0",
     "boot_menu": "yes",
+    "disk_cache": 1024,
 }
 
 def start_vm(params):