The good news is that the backup took only about 20 minutes. The bad news is that it took a lot longer to restart conlog. At startup, when it tried to add the last shutdown time to the database, it reported errors of the type: 'The total number of locks exceeds the lock table size' and quit. Adding 'innodb_buffer_pool_size=1G' to '/etc/mysql/my.cnf' and then restarting the computer seems to have fixed it, but I'm not sure what other implications this may have. I think I'm going to have to rethink how I record the shutdown times in the database.