今天去客户那里搭建DG，当创建RMAN备份集的时候，遇到了个问题，导致备份集始终无法生成，由于客户的备份集为10G左右，一次备份就要一个多小时，开始浪费了不少时间，诊断后发现，原来问题出在MAXPIECESIZE上，下面自己做了个测试，来说明这个故障现象和解决方法：
[root@ora10g ~]# su - Oracle
[oracle@ora10g ~]$ sqlplus / as sysdba
SQL*Plus: Release 10.2.0.1.0 - Production on 24 14:32:34 2014
Copyright (c) 1982, 2005, Oracle. All rights reserved.
Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Production
With the Partitioning, OLAP and Data Mining options
SQL> select open_mode from v$database;
OPEN_MODE
----------
READ WRITE
SQL> exit
Disconnected from Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Production
With the Partitioning, OLAP and Data Mining options
[oracle@ora10g ~]$ rman target /
Recovery Manager: Release 10.2.0.1.0 - Production on 24 14:32:52 2014
Copyright (c) 1982, 2005, Oracle. All rights reserved.
connected to target database: ORA10G (DBID=4175411955)
RMAN> show all;
using target database control file instead of recovery catalog
RMAN configuration parameters are:
CONFIGURE RETENTION POLICY TO REDUNDANCY 5;
CONFIGURE BACKUP OPTIMIZATION ON;
CONFIGURE DEFAULT DEVICE TYPE TO DISK;
CONFIGURE CONTROLFILE AUTOBACKUP ON;
CONFIGURE CONTROLFILE AUTOBACKUP FORMAT FOR DEVICE TYPE DISK TO '/u01/orabackup/backupsets/ora10g-%F.ctl';
CONFIGURE DEVICE TYPE DISK PARALLELISM 1 BACKUP TYPE TO BACKUPSET;
CONFIGURE DATAFILE BACKUP COPIES FOR DEVICE TYPE DISK TO 1; # default
CONFIGURE ARCHIVELOG BACKUP COPIES FOR DEVICE TYPE DISK TO 1; # default
CONFIGURE CHANNEL DEVICE TYPE DISK MAXPIECESIZE 10000 M; --最大备份集限制
CONFIGURE MAXSETSIZE TO UNLIMITED; # default
CONFIGURE ENCRYPTION FOR DATABASE OFF; # default
CONFIGURE ENCRYPTION ALGORITHM 'AES128'; # default
CONFIGURE ARCHIVELOG DELETION POLICY TO NONE;
CONFIGURE SNAPSHOT CONTROLFILE NAME TO '/u01/app/oracle/product/10.2.0/db_1/dbs/snapcf_ora10g.f'; # default
RMAN> exit
Recovery Manager complete.
[oracle@ora10g ~]$ cd /u01/orabackup/scripts/
[oracle@ora10g scripts]$ ls -l
total 4
-rwxr-xr-x 1 oracle oinstall 2443 Dec 24 14:29 backup_full.sh
[oracle@ora10g scripts]$ ./backup_full.sh
RMAN> RMAN> RMAN> RMAN> RMAN> RMAN> RMAN> RMAN> RMAN> RMAN> 2> 3> RMAN> RMAN> RMAN> RMAN> [oracle@ora10g backupsets]$ ls -lrth
total 190M
-rw-r----- 1 oracle oinstall 9.8M Dec 24 14:24 ora10g-4175411955_20141224_867162246_380.arc
-rw-r----- 1 oracle oinstall 1.7M Dec 24 14:24 ora10g-4175411955_20141224_867162255_381.arc
-rw-r----- 1 oracle oinstall 439K Dec 24 14:24 ora10g-4175411955_20141224_867162257_382.arc
-rw-r----- 1 oracle oinstall 747K Dec 24 14:33 ora10g-4175411955_20141224_867162820_384.arc
-rw-r----- 1 oracle oinstall 170M Dec 24 14:36 ora10g-4175411955_20141224_867162823_385.db
-rw-r----- 1 oracle oinstall 491K Dec 24 14:36 ora10g-4175411955_20141224_867162990_386.arc
-rw-r----- 1 oracle oinstall 7.3M Dec 24 14:36 ora10g-c-4175411955-20141224-00.ctl
[oracle@ora10g backupsets]$
根据刚才的配置，正确的生成了RMAN备份集，总大小为190M左右，其中最大的数据文件的备份集为170M，而在RMAN脚本中配置的
在备份脚本中，配置了format格式为“$ORACLE_SID-%I_%T_%t_%s.db”，以下为脚本具体的语句：
backup as compressed backupset database format '$RMAN_BACKUPSETS/$ORACLE_SID-%I_%T_%t_%s.db' tag 'db_bak' plus archivelog format '$RMAN_BACKUPSETS/$ORACLE_SID-%I_%T_%t_%s.arc' not backed up 1 times delete all input tag 'arc_bak';
当把MAXPIECESIZE的值改小，比之前最大的备份集大小（170M）还要小，比方说改成100M后，再运行之前的备份脚本，然后查看RMAN输出的日志文件，发现报ORA-27038，提示文件已经存在：
[oracle@ora10g backupsets]$ cat ../logs/rman.log |grep ORA-
ORA-19504: failed to create file "/u01/orabackup/backupsets/ora10g-4175411955_20141224_867163196_389.db"
ORA-27038: created file already exists
channel ORA_DISK_1: starting piece 2 at 2014-12-24
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03002: failure of backup plus archivelog command at 12/24/2014 14:41:52
ORA-19504: failed to create file "/u01/orabackup/backupsets/ora10g-4175411955_20141224_867163196_389.db"
ORA-27038: created file already exists
Additional information: 1