When you start Solr 6.6. and run the cloud example here's the log excerpt :
maxShardsPerNode get's set to 2 .
Compare this to Solr 7.3
So something changed and now we no longer set maxShardsPerNode and it defaults to -1 .
-1 has special handing while creating a collection ( it means max int ) . This special handling is not there while restoring a collection and hence this fails
We should not set maxShardsPerNode to -1 in the first place
Steps to reproduce:
1. ./bin/solr start -e cloud -noprompt : This creates a 2 node cluster and a gettingstarted collection which 2X2
2. Add 4 docs (id=1,2,3,4) with commit=true and openSearcher=true (default)
3. Call backup: http://localhost:8983/solr/admin/collections?action=BACKUP&name=gettingstarted_backup&collection=gettingstarted&location=/Users/varunthacker/solr-7.1.0
4. Call restore: