I've now worked at a few tech companies ranging from 10 people to ~150 and I've never encountered a real DBA. How big does a company need to get before it merits getting a DBA? What are the criteria that need to be met?
(I also posted this on Stack Overflow. It's only in both places because a moderator there suggested, "This might be one of those rare cases where it's worth it to ask on both SO and SF")
Best Answer
For a lot of companies they simply don't need a full time DBA, even if they have an inhouse database that is home built. Others need several DBAs.
As one person mentioned when the cost of losing the database is more than the salary of the DBA, then get one. That's a very good place to start. However if the database doesn't change that much, and it's on good hardware a company could probably get by for years without a full time DBA. The trick here is to have a good local (or remote) consultant to handle making sure that backups are automated and that the other database maintenance is happening on a regular basis. Have them check the system a few times a year for a health checkup and hire them to handle large projects and server upgrades and you should be fine for the most part.
As the company grows you'll end up with a more junior level guy in place to handle the more day to day stuff, but keep the consultant around if needed until it becomes worth while to pay the price for a senior level DBA.
There's no size company that needs a DBA. The company I'm at now is a small 20 person company, but we live and die by our database so hiring a senior level DBA made sense. I've got side project clients which are hundred person companies that only have an order processing system in house where the database rarely changes. I upgraded the server in 2007 and haven't been back since. I check in every few months and I'm told that the system is humming along nicely and it's backing it self up so I go on my merry way.