RMAN BACKUP FAILED ORA-19504 failed to create file AND ORA17502 ksfdcre:4 Failed to create file

RMAN BACKUP FAILED WITH RMAN-00571,RMAN-00569,RMAN-00571,RMAN-03002,ORA-19504,ORA-17502,ORA-15005.

we are getting below error in our RMAN Backup logs.

channel ch2: starting piece 1 at 15-DEC-16
channel ch2: finished piece 1 at 15-DEC-16
piece handle=+ORABKUP/matdb/backup/rman/matdb_bkp_930670803_lvl0_15_12_2016 tag=WEEKLY_FULL_BACKUP comment=NONE
channel ch2: starting piece 2 at 15-DEC-16
released channel: ch1
released channel: ch2
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03002: failure of backup plus archivelog command at 12/15/2016 15:42:51
ORA-19504: failed to create file "+ORABKUP/matdb/backup/rman/matdb_bkp_930670803_lvl0_15_12_2016"
ORA-17502: ksfdcre:4 Failed to create file +ORABKUP/matdb/backup/rman/matdb_bkp_930670803_lvl0_15_12_2016
ORA-15005: name "matdb/backup/rman/matdb_bkp_930670803_lvl0_15_12_2016" is already used by an existing alias.

Reason:

RMAN backup failed due to format specified in your RMAN backup script is not correct because backup pieces is not create with unique name using format you specified in your RMAN BACKUP Script.

To Solve this issue you need to add '%U' to guarantee generate unique file name for your backup pieces.

Example:

backup as compressed backupset incremental level 0 database FORMAT '+ORABKUP/MTDB/BACKUP/RMAN/%d_bkp_%t_LVL0_%D_%M_%Y_%U' tag 'weekly_full_backup' include current controlfile plus archivelog delete all input tag 'weekly_full_backup';

%U - Specifies a system-generated unique file name (default).

Also The meaning of %U is different for image copies and backup pieces. For a backup piece, %U specifies a convenient shorthand for
%u_%p_%c that guarantees uniqueness in generated backup file names.

More Backup format:

Format used in RMAN Backup "%d_%c_%t_%p", where :

%c Specifies the copy number of the backup piece within a set of duplexed backup pieces.

    If you did not duplex a backup, then this variable is 1 for backup sets and 0 for proxy copies.
    If a command is enabled, then the variable shows the copy number.
    The maximum value for %c is 256.

%d Specifies the name of the database.
%t Specifies the backup set time stamp, which is a 4-byte value derived as the number of seconds elapsed since a fixed reference time.
You can use a combination of %s and %t to form a unique name for the backup set.
%p Specifies the piece number within the backup set. This value starts at 1 for each backup set and is incremented by 1 as each
backup piece is created.

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