[CentOS] Setting up software IDE RAID

I have some old rack boxes which are going to get some bigger harddrives 
(IDE/ATA, not SATA) in Spring and I'm wondering if I should put two disks 
in them and use them as RAID 1 (software RAID). Objective being that the 
machine can hopefully carry on after (one) disk failure (including 
rebooting).
I don't have any experience with software RAID. Can I do this during the 
normal CentOS (4) setup or can I even do this later (when there's only one 
disk and I add another one)?
Does it make a difference performance-wise? (slight drop?)
Is it reliable, so that it will fulfill on the purpose or should I better 
forget it?
(Replacing the mainboards or adding RAID controller cards is out of the 
question.)
I'm certainly willing to read a How-To or other documentation, but since 
it's completely new to me I'm not really sure where to start searching.

Kai

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Kai Schätzl, Berlin, Germany