"In Data ONTAP 8.2 and later, a single SnapVault license is used for SnapVault primary and SnapVault secondary instead of two separate SnapVault licenses."
I undestand this is from the 8.2.2 7-mode guide but unless there were licensing changes after 8.2.2, I assume the above holds true for my ONTAP 9.1 environment, ie. only one SnapVault license is required for both primary and secondary?
Your understanding is correct. Single SnapVault license key unlocks both Primary and Secondary SnapVault.
Also Note: Beginning with ONTAP 9.1, you can use a SnapMirror license to enable SnapVault in SnapManager or SnapDrive. Those products did not allow you to use a SnapMirror license to enable SnapVault in ONTAP 9.0.
does this mean that if i buy snapvault license for one cluster, i would be able to back up (snapvault) any other cluster to this cluster ? Do i need to register a license on snapvault primary clusters ?