An often overlooked aspect of configuration is making certain there is enough space available in the archive log destination. If the database is running in archivelog mode when an online redo log file fills, Oracle’s ARCH process copies the contents of that file to the directory specified in the INIT.ORA parameter ARCHIVE_LOG_DEST. If this destination is too small, ARCH is unable to copy the log file, and once all online log files are full, the entire database stops until the situation is resolved. Experienced DBAs will immediately recognize that this condition is most likely to occur in the middle of the night, just as REM sleep has begun!