how to make a disc replica with dd ?

[Rick <rick@diabolo.bru-noc.net>]

Hello.
I have just done a big job on a machine and I want to replicate the whole
disc on an other OpenBSD machine, not same disc but about same size.
Can I do it with dd ??
Which are the preferred block size I have to use ?
Do I have to do simply

dd if=/dev/wd0c of=/dev/wd1c

being wd0 and wd1 my 2 disks ??

Do I have to do it single user and no disc mounted rite ?
OF course once this is succesfull the target disk will boot rite ?

thanks

Rick