I frequently get asked the question of how many databases a DBA typically manages. Over the past five years, I have interviewed hundreds of organizations on this topic, asking them about their ratios and how they improved them. Typically I find that the current industry average is 40 databases to a DBA for large enterprises ($1 billion+ in revenue), with the lowest ratio seen around eight and the highest at 275. So, why this huge variation? There are many factors that I see in customer deployments that contribute to this variation, such as the size of a database, database tools, version of databases, DBA expertise, formalization of database administration, and production versus nonproduction.
This ratio is usually limited by the total size of all databases that a DBA manages. A terabyte-sized database remains difficult to manage compared to a database that's 100 GB in size. Larger databases often require extra tuning, backup, recovery, and upgrade effort. The average database-to-DBA ratio is often constrained by the total size of the databases being managed, which tends to be around five terabytes per DBA. In other words, one DBA can effectively manage 25 databases of 200 GB each or five 1 terabyte databases. And these include production and nonproduction databases.
What are the factors that can help improve the ratio? Cloud, tools, latest DBMS version (automation), and DBMS product used – SQL Server, Oracle, DB2, MySQL, or Sybase. Although most DBMS vendors have improved on manageability over the years, based on customer feedback, Microsoft SQL Server tends to have the best ratios.
I believe that although you should try to achieve the 40:1 ratio and the 5 terabyte cap, consider establishing your own baseline based on the database inventory and DBAs and using that as the basis for improving the ratio over time.