OSD-04002
In this case, we tried to backup database to a specific location by formatting its path, but it failed with OSD-04002.
RMAN> backup database format 'E:\Backup\%T\RMAN-%U';
Starting backup at 16-JUN-23
...
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03009: failure of backup command on ORA_DISK_1 channel at 06/16/2023 00:38:55
ORA-19504: failed to create file "E:\BACKUP\20230616\RMAN-031UQCGU_3_1_1"
ORA-27040: file create error, unable to create file
OSD-04002: unable to open file
O/S-Error: (OS 3) The system cannot find the path specified.
OSD-04002 means that the path you specified is invalid to use, it could be non-existing, no free space or too many trivial files.
More specifically, it tells us that O/S-Error: (OS 3) The system cannot find the path specified. You should fix it then try again.
In this case, we do have E:\BACKUP, but we don't have the sub-folder, i.e. %T in the command to categorize daily backups, which is translated into a date string 20230616 at run-time.
Solutions
To solve this, the first way is to create date folders on Windows to make the destination valid for RMAN to store backup sets.
Alternatively, we can make %T to be a part of the filename instead of a folder in the path.
RMAN> backup database format 'E:\Backup\RMAN-%T-%U';
Consequently, there's no need to create a date folder in advance.