I have 9 tenants. Each tenant is about 1 TB. Could I create 1 index for each tenant? so 9 indices in total?
this would mean each index is 1 TB
9 TB of data over 9 indices. To maintain safe shard size, my index will have 48 Primaries (so each shard is 25 GB).
The ideal shard size will depend on your data as well as your queries and latency requirements. 25GB sounds like a good starting point but i would recommend running a benchmark with realistic data and queries. The result could be larger or smaller than 25GB.
The 30GB to 50GB is often recommended for time-series data queried through aggregations. If your use case is a search use case your optimum may however be quite different.