Which of the following feature is correct about the OceanStor V3 volume mirroring?

After creating a mirrored volume for a normal LUN, the server read-write IO results in a change as a result of internal information exchange.

The amount of data actually stored on a LUN is 2G, the total copy of the data is 4G. A volume image is created for the LUN, the LUN is mirrored when the copy is generated during system creation.

You can configure a volume mirror for external LUNs or configure external LUNs as mirror copies.

When configuring volume mirroring, mirror copies are required from different disk domains.