Hi @Søren Sørensen ,
that is quite a broad topic 😁
Apart from the capacity of your source to deliver, the virtual machine hosting Ingest is a critical part: you are sending (delta) parquet to the Lakehouse through that resource after all. TDI offloads that part to your VM instead of leveraging Fabric as this tends to be more cost-effective. I usually monitor CPU / RAM / disk queues to see whether there is headroom during operations, but operations on parquet tend to need both CPU and memory at the same time in rather large amounts.
Once you get into Prepare on Lakehouse, there is more of Fabric involved but I would start out making sure your VM is not restricting flow.