-run_qemu -drive driver=null-co,cache=none
-run_qemu -drive driver=null-co,cache=directsync
-run_qemu -drive driver=null-co,cache=writeback
-run_qemu -drive driver=null-co,cache=writethrough
-run_qemu -drive driver=null-co,cache=unsafe
+run_qemu -drive driver=null-co,read-zeroes=on,cache=none
+run_qemu -drive driver=null-co,read-zeroes=on,cache=directsync
+run_qemu -drive driver=null-co,read-zeroes=on,cache=writeback
+run_qemu -drive driver=null-co,read-zeroes=on,cache=writethrough
+run_qemu -drive driver=null-co,read-zeroes=on,cache=unsafe