OCP 1Z0 053 146

146.You want to take the backup of the USERS tablespace. It has a single data file of 900 MB. You have 
tape drives of 300 MB each. The SBT channel is configured for the RMAN. To accomplish the backup, 
you issued the following RMAN command: 
RMAN> BACKUP SECTION SIZE 300M TABLESPACE users; 
Which two statements are true regarding the execution of the above command? (Choose two.) 
A. The RMAN parallelizes the backup although the parallelism is not set for a channel. 
B. The backup piece size will be limited to 300 MB.  
C. The operation is accomplished using the default channel available. 
D. Three channels for the tape drive must be configured by setting the parallelism to three. 
Answer: BC 

http://docs.oracle.com/cd/E11882_01/backup.112/e10642/glossary.htm#BGBCJCBC

multisection backup

An RMAN backup set in which each backup piece contains a file section, which is a contiguous range of blocks in a data file. A multisection backup setcontains multiple backup pieces, but a backup set never contains only a part of a data file.

You create a multisection backup by specifying the SECTION SIZE parameter on the BACKUP command. An RMAN channel can process each file section independently, either serially or in parallel. Thus, in a multisection backup, multiple channels can back up a single file.

http://docs.oracle.com/cd/E11882_01/backup.112/e10642/rcmbckad.htm#BRADV89543

Dividing the Backup of a Large Data File into Sections

If you specify the SECTION SIZE parameter on the BACKUP command, then RMAN creates a backup set in which each backup piece contains the blocks from one file section. A file section is a contiguous range of blocks in a file. This type of backup is called a multisection backup.

Note:

You cannot specify SECTION SIZE with MAXPIECESIZE.

The purpose of multisection backups is to enable RMAN channels to back up a single large file in parallel. RMAN divides the work among multiple channels, with each channel backing up one file section in a file. Backing up a file in separate sections can improve the performance of backups of large datafiles.

If a multisection backup completes successfully, then none of the backup sets generated during the backup contain a partial data file. If a multisection backup is unsuccessful, then it is possible for the RMAN metadata to contain a record for a partial backup set. RMAN does not consider partial backups for restore and recovery. You must use the DELETE command to delete the partial backup set.

If you specify a section size that is larger than the size of the file, then RMAN does not use multisection backup for the file. If you specify a small section size that would produce more than 256 sections, then RMAN increases the section size to a value that results in exactly 256 sections.

To make a multisection backup:

1. Start RMAN and connect to a target database and recovery catalog (if used).

2. If necessary, configure channel parallelism so that RMAN can make the backup parallel.

3. Execute BACKUP with the SECTION SIZE parameter.

   For example, suppose that the users tablespace contains a single data file of 900 MB. Also assume that three SBT channels are configured, with the parallelism setting for the SBT device set to 3. You can break up the data file in this tablespace into file sections as shown in the following example:

   BACKUP  SECTION SIZE 300M  TABLESPACE users; 

   In this example, each of the three SBT channels backs up a 300 MB file section of the users data file.