Our philosophy moving to Azure Functions is approximately "There is no local disk. Deal with it."
We are storing 100% of data/state for our functions in a central SQL Server instance. If you provision Azure SQL in the same datacenter as the app service plan, you will see SQL commands complete in well under 5ms from the perspective of the functions. This is good enough for our purposes, especially when we consider how little time it takes to configure & manage this stack.
Our on-prem stack with SQLite running on top of local NVMe still beats the shit out of our cloud native stack in raw latency/throughput terms, but our customers spend a lot more money & time keeping these environments alive. From a user experience standpoint, the latency talking to SQL is pretty far down the list of things that you will actually feel while clicking through the views. Any perceived delays are almost always due to other systems we have to call into.
