If so, create a new database on instance A and then use GBLOCKCOPY to copy from the existing database to the new one.   Then just move the new database to instance B.

That can help sometimes. Thank you. Just move - you mean unmount and download cache.dat file?

Is this a one-time migration of data from instance A to instance B?

My question is a request for general  approaches.  But my task now is to extract some part of consistent data from the large database to use it as test data in my local database for development purposes.