how to clone a disk

[Ming Zhang <mingz@ele.uri.edu>]

Hi folks

I have a raid5 array that contain 4 disk and 1 spare disk. now i saw one
disk have sign of going fail via smart log.

so i am trying to do this

1) pull that disk (A) out
2) using dd to copy that disk (A) to another same one (B);
3) put disk (B) back to raid5 and assume that bitmap can help me resync
quickly.

now my question is 
1) can this achieve my goal?
2) is there any better/correct way?

thanks!

Ming