Elastic Pools and DTUs? How's that work?

Elastic Pools manage resource allocation to multiple Azure SQL databases.
Elastic pools may use either the DTU or vCore purchasing models, and all of their member databases use the same purchasing model as the pool. So you can't have a vCore database in a DTU Elastic Pool.
eDTUs

We refer to DTUs allocated to elastic pools as eDTUs. eDTUs aren't really a different thing than DTUs.
It's just a term to distinguish the potential capability of an elastic pool.
eDTUs simply represent the maximum number of DTUs that the elastic pool can allocate to any of its member databases within that elastic pool.
Once an eDTU has been allocated to a database, it's simply referred to as a DTU once again.

The range of pool resources that may be allocated to individual database pool members can be controlled, and the pool will automatically allocate or deallocate resources to member databases as needed within your configured per database limits.
When configuring elastic pools to use the DTU purchasing model, the Basic service tier can be used.
With elastic pools using the Basic tier, you have several different eDTU classes to choose from, which naturally affects the maximum amount of resources available to the elastic pool, not to the individual pool member databases.
The resource limits for single databases still apply to databases that are members of an elastic pool.
Single databases using Basic DTU can have no more than 5 DTUs and no more than 2 gigabytes of storage.
So while elastic pools at the Basic service tier, depending on their selected eDTU class, might have up to 16 eDTUs to allocate to their member databases and up to 156 gigabytes of total allocatable storage, each of the member databases may not be allocated more than the 5 DTUs or 2 gigabytes of storage that is allowed to a single database at that Basic class.
Elastic pools using the Basic service tier may support up to 500 member databases regardless of the selected DTU class.

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