Hi Vint,
I am from HPE Storage Team.
It is not mandatory that the source and the destination volumes should be in the same Vdisk, so you can create another vdisk using the 1.8TB drives and proceed with the volume copy.
only the condition is, the source and destination volumes should be owned by the same Controller, so it may not required to extend the Vdisk if we have the enough free space in the source vdisk for the snapshot.
when we create the volume copy for the first time, the standard volume is converted to a master
volume and a snap pool is created in the volume’s vdisk. The snap pool needs 20% of the volume size, so we should have the free space in the Source Vdisk.
In our case the volume size is 4.2 TB, so the 20% of the volume is around 860GB, please ensure the source vdisk has this free space.
If there is no free space in the source vdisk you may extend the vdisk, however the process will take long time, some times it may take days,
the recomended option is to recreate the vdisk with the additional drives and restore the backup, then you can proceed with the volume copy.
I do not see any issues related to the firmware, however its always recommended to have the latest firmware.
Please let me know if there is anything else to assist.
Thanks & Best Regards.