You don't need to be offline to make a copy of the data directory. You can do that ahead of time, keeping all the WAL segments up until the point that you make

You don't need to be offline to make a copy of the data directory. You can do that ahead of time, keeping all the WAL segments up until the point that you make the switch. (See also https://www.postgresql.org/docs/9.5/static/continuous-archiving.html#BACKUP-STANDALONE https://www.postgresql.org/docs/9.5/static/continuous-archiv...)