I just upgraded my Fedora router box with a new motherboard and CPU, the old
system had a built in RAID-controller, which I now had to replace with a
PCI-slot based Promise FastTrak100 TX2. 
When I moved the disks to the new controller I started getting messages about:

kernel: hdh: drive_cmd: status=0xd0 { Busy }
kernel: ide: failed opcode was: 0xea

The RAID5-set seems to be working fine, but as soon as you access the actual
drive, even if it's only with a "ls -l" you get the message. I also ran several
tests on the set and the data wasn't/isn't getting corrupt.

I tried to downgrade the kernel from kernel-2.6.20-1.2944.fc6 to
kernel-2.6.20-1.2925.fc6 and the messages went away.

PCI controller details:
00:0a.0 RAID bus controller: Promise Technology, Inc. PDC20270 (FastTrak100
LP/TX2/TX4) (rev 02) (prog-if 85)
        Subsystem: Promise Technology, Inc. FastTrak100 TX2
        Flags: bus master, 66MHz, slow devsel, latency 32, IRQ 16
        I/O ports at a000 [size=8]
        I/O ports at a400 [size=4]
        I/O ports at a800 [size=8]
        I/O ports at ac00 [size=4]
        I/O ports at b000 [size=16]
        Memory at dd000000 (32-bit, non-prefetchable) [size=64K]
        Expansion ROM at 50020000 [size=64K]
        Capabilities: [60] Power Management version 1

Note that I don't have the RAID-set configured in the RAID-controller, it's a
software RAID using mdadm in Fedora. The controller is just used as an IDE host
adapter for the disks.