@fiprotec

I don't have much experience in NFS sync.replication, but I think it is similar to iSCSI volume sync.replication.

You want to access the date from secondary DSS2 storage which is replicated from primary DSS1 through appropriate replication task.

This might work:
You have to:
- make sure that iSCSI volumes on DSS1 and DSS2 are consistent (see status of the replication task)
- disconnect iSCSI initiator (on client) from iSCSI target on DSS1
- stop replication task on primary DSS1.
- set iSCSI volume on DSS1 to "destination"
- set iSCSI voume on DSS2 to "source"
- make iSCSI target on DSS2 and assign this iSCSI volume to it
- connect iSCSI initiator (on client) to iSCSI target on DSS2
- You now have access to data on DSS2

When You want to go back to DSS1, You have to make
replication task on DSS2 to replicate new data from DSS2 to DSS1.
And then set similar procedure (similar to above) after replication task has status consistent.