ACID properties are not useful here. Unless every single piece of data is required, which I highly doubt, then ensuring that every single log is written correct

ACID properties are not useful here. Unless every single piece of data is required, which I highly doubt, then ensuring that every single log is written correctly doesn't matter. These are traffic logs, so if the server or application is down, how do these logs get written? I'm assuming that they don't. Have these databases never had outages as well, because if they did then the traffic would be lost as well. I would wager a guess that there are probably lots of gaps in their data that they just don't know about or don't care about. So given that not every single log is required, then you can step back from ACID requirements and find a solution that is easier to maintain. Taking 11 months to migrate a database is not reasonable for most projects.