Oracle 11g支持以sections的方式来备份和还原数据文件。在section级别进行备份，被称作multisection backup（多段备份）。section是一个数据文件中连续的块。multisection backup特性使得备份大的数据文件变得容易，可以将大文件分成多个sections，可以单独备份和还原每个section。 当面对超过32g的数据文件时，mutlisection backup特性会显著增加备份速度，因为不同的sections可以进行并行备份。每个rman的通道备份一个数据文件的不同的section。每个备份片包含一个section。
如果在备份大文件的中途失败，重启rman后可以只是备份那些尚未备份的sections。rman产生统一大小的sections，但是最后一个section可以不同。单个数据文件最多可以产生256个sections。在同一个rman备份job中，不同的数据文件可以指定不同大小的sections。
执行Multisection Backups，要手动指定section的大小，否则rman会使用默认值，默认大小的值取决与备份片的大小。
示例：
[ora11@mytest ~]$ rman target / RMAN> run{ 2> allocate channel c1 device type disk; 3> allocate channel c2 device type disk; 4> backup section size 300m tablespace yb2; 5> } using target database control file instead of recovery catalog allocated channel: c1 channel c1: SID=1 device type=DISK allocated channel: c2 channel c2: SID=40 device type=DISK Starting backup at 15-JUL-2015 12:27:10 channel c1: starting full datafile backup set channel c1: specifying datafile(s) in backup set input datafile file number=00007 name=/u11/app/oracle/oradata/ora11/yb02.dbf backing up blocks 1 through 38400 channel c1: starting piece 1 at 15-JUL-2015 12:27:20 channel c2: starting full datafile backup set channel c2: specifying datafile(s) in backup set input datafile file number=00007 name=/u11/app/oracle/oradata/ora11/yb02.dbf backing up blocks 38401 through 76800 channel c2: starting piece 2 at 15-JUL-2015 12:27:21 channel c1: finished piece 1 at 15-JUL-2015 12:27:58 piece handle=/u11/app/oracle/fra/ORA11/backupset/2015_07_15/o1_mf_nnndf_TAG20150715T122710_btcr993d_.bkp tag=TAG20150715T122710 comment=NONE channel c1: backup set complete, elapsed time: 00:00:39 channel c1: starting full datafile backup set channel c1: specifying datafile(s) in backup set input datafile file number=00007 name=/u11/app/oracle/oradata/ora11/yb02.dbf backing up blocks 76801 through 115200 channel c1: starting piece 3 at 15-JUL-2015 12:28:02 channel c2: finished piece 2 at 15-JUL-2015 12:28:02 piece handle=/u11/app/oracle/fra/ORA11/backupset/2015_07_15/o1_mf_nnndf_TAG20150715T122710_btcr9988_.bkp tag=TAG20150715T122710 comment=NONE channel c2: backup set complete, elapsed time: 00:00:41 channel c2: starting full datafile backup set channel c2: specifying datafile(s) in backup set input datafile file number=00007 name=/u11/app/oracle/oradata/ora11/yb02.dbf backing up blocks 115201 through 153600 channel c2: starting piece 4 at 15-JUL-2015 12:28:03 channel c1: finished piece 3 at 15-JUL-2015 12:28:40 piece handle=/u11/app/oracle/fra/ORA11/backupset/2015_07_15/o1_mf_nnndf_TAG20150715T122710_btcrblrs_.bkp tag=TAG20150715T122710 comment=NONE channel c1: backup set complete, elapsed time: 00:00:38 channel c1: starting full datafile backup set channel c1: specifying datafile(s) in backup set input datafile file number=00007 name=/u11/app/oracle/oradata/ora11/yb02.dbf backing up blocks 153601 through 192000 channel c1: starting piece 5 at 15-JUL-2015 12:28:40 channel c2: finished piece 4 at 15-JUL-2015 12:28:44 piece handle=/u11/app/oracle/fra/ORA11/backupset/2015_07_15/o1_mf_nnndf_TAG20150715T122710_btcrbm25_.bkp tag=TAG20150715T122710 comment=NONE channel c2: backup set complete, elapsed time: 00:00:41 channel c2: starting full datafile backup set channel c2: specifying datafile(s) in backup set input datafile file number=00007 name=/u11/app/oracle/oradata/ora11/yb02.dbf backing up blocks 192001 through 230400 channel c2: starting piece 6 at 15-JUL-2015 12:28:44 channel c1: finished piece 5 at 15-JUL-2015 12:29:11 piece handle=/u11/app/oracle/fra/ORA11/backupset/2015_07_15/o1_mf_nnndf_TAG20150715T122710_btcrcrhy_.bkp tag=TAG20150715T122710 comment=NONE channel c1: backup set complete, elapsed time: 00:00:31 channel c1: starting full datafile backup set channel c1: specifying datafile(s) in backup set input datafile file number=00007 name=/u11/app/oracle/oradata/ora11/yb02.dbf backing up blocks 230401 through 268800 channel c1: starting piece 7 at 15-JUL-2015 12:29:11 channel c2: finished piece 6 at 15-JUL-2015 12:29:18 piece handle=/u11/app/oracle/fra/ORA11/backupset/2015_07_15/o1_mf_nnndf_TAG20150715T122710_btcrcx4p_.bkp tag=TAG20150715T122710 comment=NONE channel c2: backup set complete, elapsed time: 00:00:34 channel c2: starting full datafile backup set channel c2: specifying datafile(s) in backup set input datafile file number=00007 name=/u11/app/oracle/oradata/ora11/yb02.dbf backing up blocks 268801 through 307200 channel c2: starting piece 8 at 15-JUL-2015 12:29:18 channel c2: finished piece 8 at 15-JUL-2015 12:29:21 piece handle=/u11/app/oracle/fra/ORA11/backupset/2015_07_15/o1_mf_nnndf_TAG20150715T122710_btcrdywv_.bkp tag=TAG20150715T122710 comment=NONE channel c2: backup set complete, elapsed time: 00:00:03 channel c2: starting full datafile backup set channel c2: specifying datafile(s) in backup set input datafile file number=00007 name=/u11/app/oracle/oradata/ora11/yb02.dbf backing up blocks 307201 through 345600 channel c2: starting piece 9 at 15-JUL-2015 12:29:22 channel c1: finished piece 7 at 15-JUL-2015 12:29:29 piece handle=/u11/app/oracle/fra/ORA11/backupset/2015_07_15/o1_mf_nnndf_TAG20150715T122710_btcrdror_.bkp tag=TAG20150715T122710 comment=NONE channel c1: backup set complete, elapsed time: 00:00:18 channel c1: starting full datafile backup set channel c1: specifying datafile(s) in backup set input datafile file number=00007 name=/u11/app/oracle/oradata/ora11/yb02.dbf backing up blocks 345601 through 384000 channel c1: starting piece 10 at 15-JUL-2015 12:29:29 channel c2: finished piece 9 at 15-JUL-2015 12:29:29 piece handle=/u11/app/oracle/fra/ORA11/backupset/2015_07_15/o1_mf_nnndf_TAG20150715T122710_btcrf2yk_.bkp tag=TAG20150715T122710 comment=NONE channel c2: backup set complete, elapsed time: 00:00:07 channel c2: starting full datafile backup set channel c2: specifying datafile(s) in backup set input datafile file number=00007 name=/u11/app/oracle/oradata/ora11/yb02.dbf backing up blocks 384001 through 393216 channel c2: starting piece 11 at 15-JUL-2015 12:29:29 channel c1: finished piece 10 at 15-JUL-2015 12:29:30 piece handle=/u11/app/oracle/fra/ORA11/backupset/2015_07_15/o1_mf_nnndf_TAG20150715T122710_btcrf9bk_.bkp tag=TAG20150715T122710 comment=NONE channel c1: backup set complete, elapsed time: 00:00:01 channel c2: finished piece 11 at 15-JUL-2015 12:29:30 piece handle=/u11/app/oracle/fra/ORA11/backupset/2015_07_15/o1_mf_nnndf_TAG20150715T122710_btcrf9nl_.bkp tag=TAG20150715T122710 comment=NONE channel c2: backup set complete, elapsed time: 00:00:01 Finished backup at 15-JUL-2015 12:29:30 Starting Control File and SPFILE Autobackup at 15-JUL-2015 12:29:30 piece handle=/u11/app/oracle/fra/ORA11/autobackup/2015_07_15/o1_mf_s_885126571_btcrfg3h_.bkp comment=NONE Finished Control File and SPFILE Autobackup at 15-JUL-2015 12:29:37 released channel: c1 released channel: c2 RMAN>
查看单个备份片的大小：
# du -sh o1_mf_nnndf_TAG20150715T122710_btcr993d_.bkp
300M o1_mf_nnndf_TAG20150715T122710_btcr993d_.bkp