How do DTUs in Standard and Premium performance tiers in SQL Azure compare? We recently observed a serious performance degradation in a SQL Azure database running in Standard3 performance tier - CPU utilization went from ten percent to fifty percent to almost one hundred percent in just one hour. So we changed the performance tier to Premium2 and CPU utilization immediately dropped to about eight percent.

Standard3 is claimed to offer 100 DTUs and Premium2 is claimed to offer 250 DTUs. Which means that eight percent of P2 is just twenty DTUs which is very far from using all of 100 DTUs in Standard3.

Are those DTUs different? Otherwise how is this sudden drop of utilization possible when switching from a 100 DTUs performance tier to a 250 DTUs performance tier?
I was similarly confused when looking at the pricing for those two tiers. 100 DTUs on standard costs $150/mo and 125 DTUs on Premium costs $465/mo, I figured something else must explain that disparity. I think this line from https://docs.microsoft.com/en-us/azure/sql-database/sql-database-service-tiers-dtu#choosing-a-service-tier-in-the-dtu-based-purchasing-model must explain the difference:

                            | Standard                   | Premium
IO throughput (approximate) | 2.5 IOPS per DTU           | 48 IOPS per DTU
IO latency (approximate)    | 5 ms (read), 10 ms (write) | 2 ms (read/write)


So it looks like a Premium DTU is actually worth 19x more than a Standard DTU