Nebula doesn't store data multiple times for index.

And here's how the indexing works in Nebula Graph:

You are allowed to create multiple indexes for one tag or edge type in Nebula Graph. For example, if a vertex has 5 properties attached to it, then you can create one index for each if it's necessary for you. Both indexes and the raw data are stored in the same partition with their own data structure for quick query statement scanning. Whenever there are "where" clause/syntax in the queries, the index optimizer decides which index file should be traversed.

We (I work at Dgraph) have data redundancy when you have multiple replicas for a given group - but that's an optional feature.

Thanks!