Since Oracle 10g, the value of db_file_multiblock_read_count should not be set.
On most platforms, Oracle chooses the value of db_file_multiblock_read_count such that its value multiplied by the block size is 1MB.
The following statement is likely to return 1:
select
value * (select value from v$parameter where name = 'db_file_multiblock_read_count') / 1024/1024 total_read_size_mb
from
v$parameter where name = 'db_block_size';