[U-Boot-Users] dd to generate image.

Hi, I'm using dd to generate the u-boot+kernel+rootfs image. I executed command like.. dd if=rootfs.jffs2 of=kernel.img bs=1 seek=ROOTFS_OFFSET But dd is quite slow, generating a 64MB image spends about 5 minutes. I have changed bs=1 to bs=1024 or bigger, but the outputted image size is wrong, too big. dd manpage says that bs is the size of read/write one time. Doesn't it make dd faster?

How do make dd faster?