According to millward:
I upgraded from Red Hat 7.2 to 7.3 and lost my SCSI emulation, so now cdrecord -scanbus can't find any SCSI devices and I can't use my burner. fstab has not changed from 7.2 /etc/rc.d/rc.local has /sbin/modprobe ide-scsi /sbin/modprobe sg
This should not even be required anymore, but it can't hurt. In any case, if this is the only thing you've got in there to load the drivers, then it's not enough, since at the point rc.local is run, your IDE drives have already been allocated to the IDE driver, so ide-scsi will just ignore them.
I've looked, and there is no ide-scsi in sbin
No, it's a kernel module, and would be here...
/lib/modules/`uname -r`/scsi/ide-scsi.o
In /etc/modules.conf I've got append="hdc=ide-scsi"
I hope you meant /etc/lilo.conf here... But are you still using LILO to boot your new Linux version, or have you switched to grub? In that case, you'd need to do the equivalent thing on the "kernel" line in /boot/grub/grub.conf, e.g. something like...
kernel /boot/vmlinuz-2.4.18-5 ro root=/dev/hda2 hdc=ide-scsi
(Your kernel version and root device may vary.)
I've done chmod 666 /dev/scd0 chmod 666 /dev/scd1 ( This is just a home machine so don't have to worry about security) The burner is the secondary master in the BIOS so hdc looks OK. Does this mean I'll have to do a dreaded "kernel compilation"? I've installed the 2.4.18-3 kernel source in /usr/src/ just in case, but I'm not excited about compiling kernels.
Kernel recompilations are rarely ever needed anymore with Red Hat Linux, since most drivers are set up as loadable modules. Don't recompile your kernel unless you really know what you're doing and really need some feature that's not otherwise available, otherwise you may just break other things that are working fine as is.
Is there anything else I can do to get back my scsi emulation without compiling the kernel ?
Absolutely. Try the above, and if that still doesn't work, there may be another approach to loading the ide-scsi driver which will work (similar to the way Red Hat pre-loads other SCSI drivers via ramdisk).