A Solr installation comprises 3 parts:
Here's a directory layout of a typical Solr Home directory.
| + conf | - schema.xml | - solrconfig.xml | - stopwords.txt etc | + data | - index | - spelllchecker
The 2 most important files in the Solr configuration are:
When configuring your backup scripts, the Solr Home directory is definitely what you want to backup.
You can also consider adding the conf directory to version control, rather than the whole of Solr Home (which also contains the binary index files).