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正确答案DB

这道题目没什么深入的原理，我们从答案入一一分析。

答案A不正确，多路复用可以备份在磁带和磁盘，根据经验答案不能确定是对是错的看到这种还有“only”只有唯一的单词，一般是错的。

答案B正确，镜像拷贝不支持多路径复用，实验加以验证，看下面实验：

RMAN> copy datafile 10 to '/backup/disk1/df10_1','/backup/disk1/df10_2';

RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-00558: error encountered while parsing input commands
RMAN-01009: syntax error: found "single-quoted-string": expecting one of: "archivelog, backup, controlfilecopy, current, datafilecopy, datafile"
RMAN-01007: at line 1 column 44 file: standard input

RMAN> copy datafile 10 to '/backup/disk1/df10_1';

Starting backup at 16-OCT-13
using channel ORA_DISK_1
channel ORA_DISK_1: starting datafile copy
input datafile file number=00010 name=/u01/app/oracle/oradata/ocm/tp2.dbf
output file name=/backup/disk1/df10_1 tag=TAG20131016T001904 RECID=5 STAMP=828922746
channel ORA_DISK_1: datafile copy complete, elapsed time: 00:00:03
Finished backup at 16-OCT-13

Starting Control File and SPFILE Autobackup at 16-OCT-13
piece handle=/backup/rman/c-2206937749-20131016-01 comment=NONE
Finished Control File and SPFILE Autobackup at 16-OCT-13

答案C不正确，并行度与镜像拷数无关，实验加以验证，看下面实验：

RMAN> show all;

RMAN configuration parameters for database with db_unique_name OCM are:
CONFIGURE RETENTION POLICY TO REDUNDANCY 2;
CONFIGURE BACKUP OPTIMIZATION ON;
CONFIGURE DEFAULT DEVICE TYPE TO DISK; # default
CONFIGURE CONTROLFILE AUTOBACKUP ON;
CONFIGURE CONTROLFILE AUTOBACKUP FORMAT FOR DEVICE TYPE DISK TO '/backup/rman/%F';
CONFIGURE DEVICE TYPE DISK PARALLELISM 1 BACKUP TYPE TO BACKUPSET;
CONFIGURE DATAFILE BACKUP COPIES FOR DEVICE TYPE DISK TO 1;
CONFIGURE ARCHIVELOG BACKUP COPIES FOR DEVICE TYPE DISK TO 1; # default
CONFIGURE CHANNEL DEVICE TYPE DISK FORMAT   '%U';
CONFIGURE MAXSETSIZE TO UNLIMITED; # default
CONFIGURE ENCRYPTION FOR DATABASE OFF; # default
CONFIGURE ENCRYPTION ALGORITHM 'AES128'; # default
CONFIGURE COMPRESSION ALGORITHM 'BASIC' AS OF RELEASE 'DEFAULT' OPTIMIZE FOR LOAD TRUE ; # default
CONFIGURE ARCHIVELOG DELETION POLICY TO NONE; # default
CONFIGURE SNAPSHOT CONTROLFILE NAME TO '/u01/app/oracle/product/11.2.0/dbs/snapcf_ocm.f'; # default

RMAN> CONFIGURE DATAFILE BACKUP COPIES FOR DEVICE TYPE DISK TO 2;

old RMAN configuration parameters:
CONFIGURE DATAFILE BACKUP COPIES FOR DEVICE TYPE DISK TO 1;
new RMAN configuration parameters:
CONFIGURE DATAFILE BACKUP COPIES FOR DEVICE TYPE DISK TO 2;
new RMAN configuration parameters are successfully stored

CONFIGUREDEVICE TYPE DISK PARALLELISM 1 BACKUP TYPE TO BACKUPSET;--并行度是1也没关系

CONFIGUREDATAFILE BACKUP COPIES FOR DEVICE TYPE DISK TO 2;--备份集多路径

对10文件多路径备份，这里我们的并行度为1，备份集多径路2