diff --git a/qemu/tests/cfg/usb.cfg b/qemu/tests/cfg/usb.cfg
index a20836f5e57d40eac83d7c5e533bf8dbd1aad43e..25234b7af70475112f012678f2143fc25d0b35e5 100644
--- a/qemu/tests/cfg/usb.cfg
+++ b/qemu/tests/cfg/usb.cfg
@@ -187,6 +187,7 @@
         - usb_storage:
             type = usb_storage
             images += " stg"
+            blk_extra_params_stg = "serial=TARGET_DISK0"
             image_boot_image1 = yes
             image_name_stg = "images/usbdevice"
             image_format_stg = "qcow2"
diff --git a/qemu/tests/format_disk.py b/qemu/tests/format_disk.py
index 4d1a11dd49ce3d77406763dae9b96d879094b9aa..c184515160ae00ccd70a94ae0659ee8dc2f347a9 100644
--- a/qemu/tests/format_disk.py
+++ b/qemu/tests/format_disk.py
@@ -37,6 +37,12 @@ def run(test, params, env):
     if params.get("os_type") == 'linux':
         drive_name = params.objects("images")[-1]
         drive_id = params["blk_extra_params_%s" % drive_name].split("=")[1]
+        # If a device option(bool/str) in qemu cmd line doesn't have a value,
+        # qemu assigns the value as "on".
+        if drive_id == "NO_EQUAL_STRING":
+            drive_id = "on"
+        elif drive_id == "EMPTY_STRING":
+            drive_id = ""
         drive_path = utils_misc.get_linux_drive_path(session, drive_id)
         if not drive_path:
             raise error.TestError("Failed to get '%s' drive path" % drive_name)
diff --git a/qemu/tests/usb_storage.py b/qemu/tests/usb_storage.py
index 8ecbc8e2785073c4144ac16f8dd7bdba72fae83b..9285224a8b1d3b8d4174b85b06e9fa3fcc68284e 100644
--- a/qemu/tests/usb_storage.py
+++ b/qemu/tests/usb_storage.py
@@ -95,11 +95,10 @@ def run(test, params, env):
         if vm.is_alive():
             vm.destroy()
 
-        new_params = params.copy()
         for option, value in options.iteritems():
-            new_params[option] = value
+            params[option] = value
         error.context("Restarting VM")
-        vm.create(params=new_params)
+        vm.create(params=params)
         vm.verify_alive()
 
     def _login():
@@ -123,7 +122,7 @@ def run(test, params, env):
     @error.context_aware
     def _check_serial_option(serial, regex_str, expect_str):
         error.context("Set serial option to '%s'" % serial, logging.info)
-        _restart_vm({"drive_serial_stg": serial})
+        _restart_vm({"blk_extra_params_stg": "serial=" + serial})
 
         error.context("Check serial option in monitor", logging.info)
         output = str(vm.monitor.info("qtree"))