How do you organize the Photo Archive at work?

Question

Computer networks

What is:
- folders with photos, about 3 TB + 1 TB annually (JPG + CR2 format)
- stored on the network, accessed via SMB from Windows machines (Debian server)
- now the photos are split \year\event\ , for example \2015\Graduation_meeting , folders come from 2005
- about 10 people work with the server at the same time
Problem:
You often need to find old photos of a certain subject
What you want: The ideal solution is to buy 10 lightroom licenses and not worry, but there is no money. Therefore, I want a software that can massively tag photos, has a pre-simple photo, tag history, and can work with RAW. (Do not offer Adobe bridge, it only comes in the package). Or tell me how you solve a similar problem.