When are full time DBAs necessary?

If you are a small to medium sized business, is a full time database administrator (DBA) completely necessary? Would having DBA consultants work better to use them as needed? Here are some factors to consider around this:

Application development. New databases or tables will need to be planned / designed / created as you add new applications or functionality to your stack. How often are these services needed? Do your developers have the necessary DBA skills and knowledge to be doing this kind of design and planning work?

Database maintenance. Depending on the database technologies you use, some may have more maintenance which needs to be completed on them at regular intervals. Can you switch technologies to minimize this effort? What kind of changes can you make to your existing database to better stabilize it so less maintenance is needed?

Data corruption and consistency. There will be times when applications will incorrectly or partially write data to the databases. When this happens do you have the operational support and knowledge in house to be able to fix these problems?

Data monitoring and health. Best practice is to know when the data in your databases is incorrect proactively. Do you have in house skills who can write these monitors, understand the data structures, and write code to ensure the health of your data consistency?

Legacy applications. If you have a legacy application stack oftentimes the database can have size and performance issues depending on how correctly or not it was setup. If you have a maintenance intensive database from these issues it might be worth keeping a full time DBA on hand.

Consider all of the factors listed. Would you spend more time in house using existing the knowledge and skills of your staff to be solving these problems that amounts to a full time position? If not budget out the hours you predict will be needed to use consultants to fill the gap. Lastly the cheapest solution would be to ensure your future hires have the database skills you need to design and maintain your databases with no additional assistance needed.