Machine type is permanent
Shared core machines are good for prototyping and are not covered by Cloud SLA
Each vCPU is subject to a 250 MB/s network throughput cap for peak performance. Each additional core increases the network cap, up to a theoretical maximum of 2000 MB/s
For performance-sensitive workloads such as online transaction processing (OLTP), a general guideline is to ensure that your instance has enough memory to contain the entire working set and accommodate the number of active connections
SSD (solid-state drive) is the best choice for most use cases. HDD (hard-disk drive) offers lower performance, but storage costs are significantly reduced, so HDD may be preferable for storing data that is infrequently accessed and does not require very low latency.
There is a direct relationship between the storage capacity and its throughput.