It is not currently possible to disable logging on the ruby mongo driver when using Mongoid. Disabling the logger in the config block does not work:

Mongoid.configure do |config|
config.from_hash(settings[ENVIRONMENT])
config.logger = nil
end

nor does just setting Mongoid.logger to nil. The ruby mongo driver continues to output the warning:
"MongoDB logging. Please note that logging negatively impacts performance and should be disabled for high-performance production apps"

It is desirable to turn off logging completely in production, not set to a logger with a low priority. The fundamental problem appears to be the is the logger method in mongoid/config.rb:

def logger
@logger ||= defined?(Rails) ? Rails.logger : ::Logger.new($stdout)
end

The ||= is causing a logger set to nil to always be set to a new logger. Ideally Mongoid would disable logging on the ruby driver by default making it explicit to enable if needed. The performance penalty of enabling logging is generally undesirable.