Amar,
I read the articles you posted, and thought I'd test it out. My results were not what I expected.

Large Pool = 80M
Block Size = 16K
db_file_direct_io_count = 128
Files = 9
Backup_tape_io_slaves = true
Backing up directly to tape.

From the first article, my memory usage should be:
memory(input) = 4 * #files * db_block_size * db_file_direct_io_count
= 4 * 9 * 16*1024 * 128
= 72 Meg

Code:
SQL> select * from v$sgastat where pool ='large pool';

POOL        NAME                            BYTES
----------- -------------------------- ----------
large pool  free memory                  80000000

SQL> /
While the backup is running, it only used 278K of the large pool.

Code:
POOL        NAME                            BYTES
----------- -------------------------- ----------
large pool  free memory                  79721424
large pool  KSFQ Buffers                   278576
What am I missing?

Thanks!
Jodie