|Redis stores everything in primary memory.
||RDBMS stores everything in secondary memory.
|In Redis, Read and Write operations are extremely fast because of storing data in primary memory.
||In RDBMS, Read and Write operations are slow because of storing data in secondary memory.
|Primary memory is in lesser in size and much expensive than secondary so, Redis cannot store large files or binary data.
|| Secondary memory is in abundant in size and cheap than primary memory so, RDBMS can easily deal with these type of files.
|Redis is used only to store those small textual information which needs to be accessed, modified and inserted at a very fast rate.
If you try to write bulk data more than the available memory then you will receive errors.
|RDBMS can hold large data which has less frequently usage and not required to be very fast.