in couchbase 1.8.1 release we did modify the logging mechanism from binary into text format.
right now under /var/lib/couchbase/logs user will observe log.* , error.* and info.* log files and each log file can grow up to 20MB.
maximum number of log files are 20 so after running cluster for a while user might see 600 MB ( 3*2*20MB ) files in logs folder