The Global Mirror Copy Service provides an asynchronous copy, which means that the secondary virtual disk (VDisk) is not an exact match of the primary VDisk at every point in time.
The host application writes data to the primary VDisk and receives confirmation that the write operation is complete before the data is actually written to the secondary VDisk. This feature is comparable to a continuous backup process in which the last few updates are always missing. When you use Global Mirror for disaster recovery, you must consider how you want to handle these missing updates.
If I/O operations on the primary VDisk are paused for a small length of time, the secondary VDisk can become an exact match of the primary VDisk.