mkfs.cramfs block size problem

[Junior <ejr@inbox.com>]

Hi All,
I'm creating a cramfs using the following command:

mkfs.cramfs -v -b 0x20000 filesystem root.cramfs

without the -b the cramfs is created, however with the -b option it does not seem to reconize this option and it printing the usage format.

I tried the -b option with -b 128k, -b 256K etc. and although the command executed, the cramfs size is much larger than expected, infact larget than the jffs2 fs. 

What is the default block size for cramfs?
Isn't this the correct usage?

Much thanks,
--Jr.