You can try:
dd if=/dev/sda of=/dev/sdb bs=4096 conv=notrunc,noerror
Note the difference. sdb will now be an image of sda.
The problem with copying a whole disk to a partition is that the partition definitions get lost as they become data blocks on the destination partition. You no longer have valid filesystems on sdb1, instead, the blocks that would have become the filesystem header will be the partition table copied from sda. Now, this IS similar to an extended partition, but because it is copied from sda, the partition is not identified as an extended partition, and may have a slightly different layout.