Hi Marco -
NetApp TR-4052 (here) has great information on this scenario. The basics of the issue are covered in the NetApp feature summary section on page 53. A recommended solution is at the bottom of page 35 onto page 36.
The guts of it: because SnapVault is qtree based in 7-mode and whole volume based in cDot, a direct migration isn't possible. So the recommendation is convert and migrate the source, create a new SnapVault relationship going forward, and either preserve (short term) the original vault or SnapMIrror the original vault volume to a new 64 bit "legacy SnapVault" volume on the new cDot system as well. The new SnapVault will protect going forward but does require a new baseline. The legay SnapVault will be available for restores - manual process involved. Snapshots will need to be retired manually from the legacy SnapVault volume as well as they would fall off retention.
Fundamentally - you're going to need a new SnapVault in either case, but there is a way at least to bring the old version with you. The TR covers a number of typical scenarios that need special handling. You may find there is something that better fits your situation.
Hope this helps.
Bob Greenwald
Senior Systems Engineer | cStor
NCIE SAN ONTAP, Data Protection
Kudos and accepted solutions are always appreciated.