Hi Tim,
The 2dshere version 3 index created in MongoDB v3.2 is not compatible with MongoDB v3.0. MongoDB v3.0 will not start and throw you an error similar to :
2016-02-15T09:48:21.219+1100 I STORAGE [initandlisten] exception in initAndListen: 17395 unsupported geo index version { 2dsphereIndexVersion : 3 }, only support versions: [1,2], terminating
However, if you are upgrading from v3.0 to v3.2 existing 2dsphere version 2 index should work fine in v3.2.
Remember to always backup all of your data before upgrading MongoDB. Also see:
Regards,
Wan.
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