[plug] "dd" question

[Steege, Phil E]

I want to "clone" my hard drive to a spare hard drive, of equal size.
This was cheaper than going out and paying for a tape drive that could
handle 40GB disks.

The dd command man page says there are different block sizes.  Which block
size (bs) quantity is right for Linux.
I was going to use the following command " dd if=/dev/had of=/dev/hdb bs=512
".
Would that be correct ?

I thought about RAID (software raid) using a mirror (raid 1) configuration,
but I have no experience with RAID.
I figured I would just run a nightly cron job with the dd command.

Phil