Are both Redis Database and Redis Cache stored in memory and not on disk?
If so what are the major differences between them?
If both are stored in memory only then there should not be much difference between them in speed.
Do we still need Cache?
What are their advantages?
Can the server restart remove all data in the Redis database?
The cache must be deleted.
Redis is a product first of all. It's an in-memory data structures store.
Depending on its configurations it can be targeted to different use cases:
Cloud providers can call this "Cache" meaning that they offer a Redis that is pre-configured to be used as a cache (remove the oldest records when the memory becomes next to be fully utilized, etc). But after you will work with some kind of Redis client that will interact with a remote Redis server.