From the DOT release notes;
Major nondisruptive upgrades for MetroClusters
Data ONTAP 7.3.2 introduces the ability to upgrade fabric-attached MetroClusters from one release
family to another nondisruptively (major nondisruptive upgrades). Data ONTAP 7.3 introduced the
ability to upgrade stretch MetroClusters from one release family to another nondisruptively.
For more information about fabric-attached and stretch MetroClusters, see the
Data ONTAP Active/Active
Con
figuration Guidefiguration Guide.For more information about nondisruptive upgrades, see the
figuration Guide
Data ONTAP Upgrade Guide.