rebalanceMovesBeforeCompaction is the parameter that customers can use during rebalance to improve rebalance speeds but at the cost of index file size.
wget --post-data='rebalanceMovesBeforeCompaction=256' --user=Administrator --password=asdasd http://lh:9000/internalSettings
So that's usual POST to usual /internalSettings API with field name rebalanceMovesBeforeCompaction.
Default value is 16. And that's how many in- or out- going vbuckets will be moved per node before pausing all moves, triggering views compaction and awaiting its completion.
View compaction is forbidden during vbucket moves. So larger values means less frequent view compactions. Which means less time "spent" on it, but it also means greater disk usage by views.
For additional info ping Alk, Pavel.