ORA-01126: database must be mounted in this instance and not open in any instance

There are certain administration tasks that need database to be mounted, not open, while performing the task, otherwise ORA-01126 would be returned. In the following I am explaining one of those operations that returned me ORA-01126 because I had my database open while converting my database to archivelog mode.

RMAN-03009 and ORA-19510: failed to set size of 92079 blocks for file

If you RMAN backup commands are failing with RMAN-03009 with ORA-19502 and ORA-19510, it is because your destination file system has no space left on it for the backup. You need to make sure that file system where you are storing backup should have sufficient space to host the backup. Output of command may be similar to the following