Usually, Lucene 7.0.0 is not compatible with 5.5.0, such as (Lucene 7.0.0 read indexes created by Lucene 5.5.0)
Format version is not supported (resource BufferedChecksumIndexInput(MMapIndexInput(path="F:\segments_1"))): this index is too old (version: 5.5.0). This version of Lucene only supports indexes created with release 6.0 and later.
And ES create indexes based on Lucene, is it means, if Lucene's indexes compatible with old version then es also compatible, if Lucene's indexes not compatible with old version then es not compatible either. In another word, es always be consistent with Lucene's compatibility behavior？
By the way, does ES use https://en.wikipedia.org/wiki/Consistent_hashing consistent hashing algorithm to implements data balance?