Db2 image copy offload use case process consists 1) create PIT Db2 image copies using DSS and FlashCopy, and 2) execute HSM command-based migration. 

• Do all Db2 tables/partitions have to live in the same DS8000, or can they live in multiple DS8000?

Hi Toy, DSS FlashCopy requires a data set (table) to reside on a single device.  When processing multiple data sets, they can reside on multiple DS8000s. 

The TCT migration itself does not require a data set to reside on a single DS8000.  A multi-volume data set spread across multiple DS8000s can be migrated with TCT.  It will be recalled back to a single DS8000.