Minor Description
JIRA for Jan's comments on SOLR-6513:
I thought we agreed to prefer the term "shard" over "slice", so I think we should do this for this API as well.
The only place in our refguide we use the word "slice" is in How SolrCloud Works [1] and that description is disputed.
The refguide explanation of what a shard is can be found in Shards and Indexing Data in SolrCloud [2], quoting:
When your data is too large for one node, you can break it up and store it in sections by creating one or more shards. Each is a portion of the logical index, or core, and it's the set of all nodes containing that section of the index.
So I'm proposing a rename of this API to BALANCESHARDUNIQUE and a rewrite of [1].
[1] https://cwiki.apache.org/confluence/display/solr/How+SolrCloud+Works
[2] https://cwiki.apache.org/confluence/display/solr/Shards+and+Indexing+Data+in+SolrCloud
Note Mark's comment on that JIRA, but I think it would be best to continue to talk about "shards" with user-facing operations.