SQL Server 2008: How to query all databases sizes?

Question

I have MS SQL 2008 R2, 500 databases. What is the most efficient, easiest and \'modern\' way to query all databases sizes.

The output should have columns:

Answer 1

All this examples work fine on most of my database servers. However if you have 1 server with multiple instances and all those servers those query's give you no result.

For instance the first query gives a result like:

name    DataFileSizeMB  LogFileSizeMB
master  NULL    NULL
tempdb  NULL    NULL
model   NULL    NULL
msdb    NULL    NULL

So the databases are selected from sys.databases, however the table sys.master_files seems to be empty or gives no result.

Even a simple query as select * from sys.master_files has a result of 0 records. You don't receive any errors but no records are found. On my servers with only 1 database instance this works fine.