Usage: CHAN <room> LOG ON <filename> [directory|file]

This will turn logging on for a room. The room will log to the file you set with the PARAM command. You must have a bot in the room to do the logging. This is only available in the Enterprise edition or with the Scribe module.

/as chan #chat log on

This is an easy way to keep records of all the activity in a room. The bot will log everything it sees in the room, which means so long as there are no splits all conversation in the room will be logged. If it is important to make sure that nothing is missed you can have a bot on each server logging, assuming they are Enterprise servers or have the Scribe module.