I am thinking of running multiple database/messages servers such as postgres, redis, mongo, influxdb on old computers and use a centralized NAS to store the data.
One advantage is that I don’t need to worry about getting appropriate local storage for the computers that host these services. For example, I could run postgres on an old desktop with spinning disks or even a raspberry pi.
But I am still concerned about the I/O speed and reliability. I wonder if anyone has experience doing it like this. Can you share the pros and cons? I really appreciate it.
You can compensate the higher latency with keeping most or all of the database in memory (at least with postgres or mysql) aka caching. This will help you with database reads but not with writes. Writes need to hit a persistant storage layer first. When it comes to reliability I usually rely on the replication features shipped by the DBMS.
Here is an in depth blog about local and distributed storage with MySQL. https://blog.koehntopp.info/2022/09/27/mysql-local-and-distributed-storage.html
Can´t really say much about other types of databases though.