@@ -57,6 +57,7 @@ class QCowUtil(CowUtil):
     QCOW2_MAGIC = 0x514649FB  # b"QFI\xfb": Magic number for QCOW2 files
     QCOW2_HEADER_SIZE = 104  # In fact the last information we need is at offset 40-47
     QCOW2_BACKING_FILE_OFFSET = 8
+    QCOW2_INCOMPATIBLE_FEATURE_EXTENDED_L2 = 0x10
 
     def _read_qcow2(self, path: str):
         with open(path, "rb") as qcow2_file:
@@ -100,6 +101,7 @@ def _read_qcow2_header(file: BinaryIO) -> Dict[str, Any]:
         # refcount_table_clusters: u32, // Number of clusters for the refcount table
         # nb_snapshots: u32,            // Number of snapshots in the image
         # snapshots_offset: u64,        // Offset to the snapshot table
+        # incompatible_features: u64,   // Bitmask of incompatible features
 
         file.seek(0)
         header = file.read(QCowUtil.QCOW2_HEADER_SIZE)
@@ -117,7 +119,8 @@ def _read_qcow2_header(file: BinaryIO) -> Dict[str, Any]:
             _,
             _,
             snapshots_offset,
-        ) = struct.unpack(">IIQIIQIIQQIIQ", header[:72])
+            incompatible_features,
+        ) = struct.unpack(">IIQIIQIIQQIIQQ", header[:80])
 
         if magic != QCowUtil.QCOW2_MAGIC:
             raise ValueError("Not a valid QCOW2 file")
@@ -135,6 +138,7 @@ def _read_qcow2_header(file: BinaryIO) -> Dict[str, Any]:
             "refcount_table_offset": refcount_table_offset,
             "snapshots_offset": snapshots_offset,
             "parent": parent_name,
+            "incompatible_features": incompatible_features,
         }
 
     @staticmethod
@@ -246,6 +250,9 @@ def _add_or_find_custom_header(self) -> int:
 
             return custom_data_offset
 
+    def _convert_bool_to_qemu_option_value(self, option: bool) -> str:
+        return 'on' if option else 'off'
+
     # ----
     # Implementation of CowUtil
     # ----
@@ -263,6 +270,11 @@ def getBlockSize(self, path: str) -> int:
         self._read_qcow2(path)
         return 1 << self.header["cluster_bits"]
 
+    @override
+    def getExtendedL2(self, path: str) -> bool:
+        self._read_qcow2(path)
+        return bool(self.header["incompatible_features"] & self.QCOW2_INCOMPATIBLE_FEATURE_EXTENDED_L2)
+
     @override
     def getFooterSize(self) -> int:
         return 0
@@ -282,7 +294,7 @@ def calcOverheadEmpty(self, virtual_size: int, block_size: Optional[int] = None)
             cluster_size = block_size
         else:
             cluster_size = QCOW2_DEFAULT_CLUSTER_SIZE
-        cmd = [QEMU_IMG, "measure", "-O", "qcow2", "--output", "json", "-o", f"cluster_size={cluster_size}", "--size", f"{virtual_size}"]
+        cmd = [QEMU_IMG, "measure", "-O", "qcow2", "--output", "json", "-o", f"cluster_size={cluster_size},extended_l2=on", "--size", f"{virtual_size}"]
         output = json.loads(self._ioretry(cmd))
         return int(output["required"])
 
@@ -636,9 +648,11 @@ def snapshot(
         if parentRaw:
             parent_type = RAW_TYPE
             cluster_size = QCOW2_DEFAULT_CLUSTER_SIZE
+            extended_l2 = False
         else:
             parent_type = QCOW2_TYPE
             cluster_size = self.getBlockSize(parent)
+            extended_l2 = self.getExtendedL2(parent)
         args = ["-f", QCOW2_TYPE, "-F", parent_type, "-b", parent]
 
         if is_mirror_image:
@@ -650,9 +664,9 @@ def snapshot(
             # Ensuring we go back to a better cluster_size for performance reasons.
             # This limit our images max size to 64TiB.
             cluster_size = 16 * 1024 # 16KiB
-            args.extend(["-o", "extended_l2=on"])
+            extended_l2 = True
 
-        args.extend(["-o", f"cluster_size={cluster_size}"])
+        args.extend(["-o", f"cluster_size={cluster_size},extended_l2={self._convert_bool_to_qemu_option_value(extended_l2)}"])
         cmd.extend(args)
         cmd.append(path)