Bryan wants a bit more insight:
System was running Centos 3 and had 3 PATA drives - one containing root, boot, swap and then a mirrored pair for our data. CentOS 4 wasn't around when the server was initially setup.
The mirrored pair were running off a PCI controller with an ITE 8212 chipset which was a real pain in in the ass to get going - I recall compiling the driver and adding it to the boot image manually.
Anyway, along comes Mr Electrical Inspection and - allegedly - leaves the server well alone while testing **ALL** other equipment in the office. Now, as soon as Mr E.I. leave site everyone amazingly discovers that the server is 'down'.
When I arrive on site the server is 'hung' with no image on the monitor. I power cycled it and rebooted - had to fsck root but got an error that the RAID array was damaged and I was being dropped to a repair console (or words to that effect). At that stage absolutely everything I did to try and repair the drives resulted in an error and would not touch the drives on the 8212-based controller at all.
Now, the reason we had 3 drives in the system originally was because I could not get the system to boot from a drive on the 8212 controller and with one disk on the motherboard's controller and one on the 8212 the whole lot was unstable so we ended up as described above.
When I started to have problems re-mounting the RAID drives I just 'bit the bullet' and decided to put CentOS 4 on a spare 80GB drive I'd bought with me because I knew that the 8212 controller was supported natively and it was something I was going to do at a 'convenient' time anyway - I also guessed it would be quicker and more worthwhile than fiddling with the CentOS 3 installation. The plan was also to end up with just two disk drives in the system, as originally intended, but I didn't want to (and couldn't) mess around with the RAID pair until I had CentOS4 up and running.
The system was Running CentOS4 in about 20 mins, I mounted one of the RAID drives, checked it out, copied all wanted data onto the 'new' primary disk and got the users running their company management system as soon as possible as this was the #1 priority.
After that I reinstalled the email system (postfix, MailScanner, clamAV etc. - thanks again for the excellent walk through Johnny) and did a general tidy up knowing that I could now get back on the system from my office to tidy up (caching name server, nntp time sync and a few 'home' mappings.
That's it - all that's left to do it mirror the current (one) drive as mentioned in my original email.
Hope that's all clear. If anyone wants to comment on what I did I'd be happy to hear what you think and perhaps what I might have done differently!
Nigel