Which two actions would you take for tape streaming to happen during the backup?

Answer: E,F
http://docs.oracle.com/database/121/BRADV/rcmtunin.htm#BRADV90072

It’s B and E

Write Phase for System Backup Tape (SBT)
When backing up to SBT, RMAN gives the media management software a stream of bytes and associates a unique name with this stream. All details of how and where that stream is stored are handled entirely by the media manager. Thus, a backup to tape involves the interaction of both RMAN and the media manager.

RMAN Component of the Write Phase for SBT
The RMAN-specific factors affecting the SBT write phase are analogous to the factors affecting disk reads. In both cases, the buffer allocation, slave processes, and synchronous or asynchronous I/O affect performance.

Allocation of Tape Buffers
If you back up to or restore from an SBT device, then by default the database allocates four buffers for each channel for the tape writers (or reads if restoring data as shown in Table 23-1). The size of the tape I/O buffers is platform-dependent. You can change this value with the PARMS and BLKSIZE parameters of the ALLOCATE CHANNEL or CONFIGURE CHANNEL command.

Tuning the Read Phase
RMAN may not be able to send data blocks to the output device fast enough to keep it occupied. For example, during an incremental backup, RMAN only backs up blocks changed since a previous data file backup as part of the same strategy. If you do not turn on block change tracking, then RMAN must scan whole data files for changed blocks, and fill output buffers as it finds such blocks. If few blocks changed, and if RMAN is making an SBT backup, then RMAN may not fill output buffers fast enough to keep the tape drive streaming.

You can improve backup performance by adjusting the level of multiplexing, which is number of input files simultaneously read and then written into the same RMAN backup piece. The level of multiplexing is the minimum of the MAXOPENFILES setting on the channel and the number of input files placed in each backup set. The following table makes recommendations for adjusting the level of multiplexing.

Table 23-3 Adjusting the Level of Multiplexing

ASM Striped Disk Recommendation
No

Yes

Increase the level of multiplexing. Determine which is the minimum, MAXOPENFILES or the number of files in each backup set, and then increase this value.

In this way, you increase the rate at which RMAN fills tape buffers, which makes it more likely that buffers are sent to the media manager fast enough to maintain streaming.

No

No

Increase the MAXOPENFILES setting on the channel.

Yes

Not applicable

Set the MAXOPENFILES parameter on the channel to 1 or 2.