See What is a Solr collection/core/shard/replica? for help in distinguishing these critical Solr concepts.
Standard backups in SearchStax Cloud rely on the principle that every Solr node contains a replica of every collection. Therefore, it is sufficient to back up one node while the remaining nodes continue to serve queries.
A sharded collection splits the index across multiple nodes. Backing up one node does not capture the full index.
For this reason, SearchStax Cloud has built-in safeguards against backing up a sharded collection. If SearchStax Cloud detects sharding, it will refuse to proceed.
Some of our Platinum and Platinum Plus clients require sharded collections. For them, we can implement custom backup solutions through a Service Request. Please contact SearchStax Support to explore this option.