I successfully installed FC4 on a PII-333smp machine (Intel mboard), using two 
mirrored RAID1 18GB SCSI drives aic7xxx.  I also have two Promise Ultra 100 TX2 
controllers, with 4 160GB PATA hard drives connected as master to each of four 
IDE channels, partitioned as RAID autodetect and recognized as hde, hdg, hdi, 
hdk.  I created a RAID5 array md4 with these 4 drives using mdadm, was able to 
format it (jfs filesystem in this case) and mount it (I created a mount point 
called /data, and modified fstab appropriately).  I was able to copy data to 
it, unmount and remount the volume, and inspection of /proc/mdstat showed the 
array to be normal.  When I rebooted the machine the array disappeared, no 
trace of md4, and using mdadm --scan resulting in an error message saying the 
array did not exist.  I have now discovered that the partion tables for all 
four drives have been erased.  This is repeatable, I did it twice.  The RAID1 
array on aic7xxx is unaffected, but the system crashed the first reboot while 
it tried to mount a non-existant RAID array (this is another serious bug!  the 
system should gracefully recover if it can't mount an external filesystem!). 
The second time I refrained from modifying fstab until I verified the problem.  
I followed the mdadm guidance explicitly, and cannot make this work, there are 
no existing bug reports on this subject.  I can do this task in Windows 
2000/XP/2003 within five minutes, why is it so difficult to create a RAID5 
array in Linux?  Chris Cantwell