What number of bytes should I set the bs to in the dd command?

Question

I have just created a usb boot disk so that I can install Fedora 14.

I used the following which was successfully. However, I am left wondering what does the bs parameter actually does. I know it mean bytes and copies these at a time. But how do I know what to set it to?

dd if=F14-Live-i686.iso of=/dev/sdb bs=8M

In the above example it is set to 8MB. However could I set this to any value that I want?

Many thanks for any advice,

Answer 1

it stands for block size - its simply how many blocks are read and written at a time. Larger block sizes are faster, but if an error occurs, you'd need to redo the whole block

The optimum blocksize apparently depends on the buffer size for a hard disk - no one seems to know for sure for a external drive

I'd refer you to this and this for further reference