I use kopf for visualization, and I tried changing the number of replica setting for an index from 17 to 20, making the replication group of 21 using kopf. (total 20 primary shards + 3 availability zones)
The observation is, it assigns some number of replica's (mainly group of 60) but others stay unassigned. Any pointers on debugging this issue ?
Elasticsearch version 1.7

---
NEW: Monitor These Apps!
elasticsearch, apache solr, apache hbase, hadoop, redis, casssandra, amazon cloudwatch, mysql, memcached, apache kafka, apache zookeeper, apache storm, ubuntu, centOS, red hat, debian, puppet labs, java, senseiDB