SOLR-11063 added disk space hint to Policy. The ADDREPLICA, MOVEREPLICA, SPLITSHARD and REPLACENODE APIs can provide this hint.
- ADDREPLICA can query the size of the leader's data direcoty for the same shard and pass it to policy
- MOVEREPLICA again knows the size of the replica being moved
- REPLACENODE can compute the sum of disk usage of all the replicas' data directories
We should probably include both index and tlog size in the hint to ensure that we have ample space on target nodes.
We should also take care of HDFS because for movereplica and replacenode, there are no disk space requirements because the original replica's HDFS data and ulog directories are used by the new replicas.