Please search through these DI forums, as this question has been asked before.
Broadly speaking:
The answer, like always, is “it depends”. 3M rows per day isn’t that big a deal, but it depends if that’s in 1 table or in 100 tables. Depends on the complexity of the ETL job. Depends on the size/width of those tables being loaded. And so on.
If you have a reasonably-sized DI server, then the bottleneck is more likely to be with the database servers involved.
If you can, put DI on the same server as your target database server.
What is your current environment/specs? And what is the performance? Doing the benchmark comparison as suggested above may help tell you how your environment will perform relative to others.