[CentOS] Mirroring Hard Drive

>> I have a 500GB Sata drive about 15% used I would like to make an exact
>> copy of too another Sata 500GB drive as a spare.  That way if
>> something happens to the one in service I can plug in the spare
>> quickly and restore one of the weekly backups without reinstalling the
>> entire OS and all the little tweaks of setup on this mail/web server.
>>
>> How do I do this?  That is make an exact bootable copy of a linux
>> drive.  Its running Centos 4.6 if that matters.
>>
>
> stupid question ... why not just put it in the machine and make it a raid1
> mirror
>
> then, if the first one dies, you just use the second one :D

How do you do that?

Matt