Hi all,

I need some help from a guru. I have combo CD-RW/DVD drive. If I want to have a smooth dvd playback, I must have ide-scsi emulation disabled. In order to burn CDs, I need it enabled. I know how I can enable ide-scsi with kernel parameters at boot time. I just rather not reboot just b/c I want to burn a CD, or just because i want to watch a dvd.

Apparently, there is a way to accomplish this so long as ide-cd is compiled as a module which it is in mdk9.1. Ide-scsi is compiled as a module as well. I got some instructions here:
http://www.linuxdocs.org/HOWTOs/SCSI-2.4-HOWTO/sr.html
basically,
rmmod ide-scsi; rmmod ide-cd; modprobe ide-scsi

It doesn't work

When I boot with no ide-scsi emulation, then when I try to enable it, the cd drive does not appear anywhere in the dev file system. similarly, when I load with ide-scsi enabled, I cannot disable it - well I can, but only by not having any access to the drive: rmmod ide-scsi gets rid of the scd0 entry but modprobe ide-cd does not give me the hdc entry I should get...

Any thoughts what might be missing? It seems I'm on the right track

I'm not sure but do you have an entry in /etc/fstab for two drives?

like /dev/cdrom and /dev/cdrom0, then you would use one for cd drive and the other one for dvd drive.

Maybe that could be a problem if you don't have it. Try it to see what happens!

the fstab file is ok. The trouble is that I don't get the dev files in the first place.
When I start with no ide-scsi, I can 'detach' the drive by rmmod ide-cd. I can re-attach it to /dev/hdc by modprobe ide-cd. I am supposed to be able to attach it as a scsi-drive by doing modprobe ide-scsi but this part is not working. It's as though it's not detecting the drive.

im in your shoes too.

all i had to do is to boot with ide-scsi off and then reboot with ide-scsi on. The drive now appear as
/dev/ide/etc.etc.
and
/dev/scsi/etc.etc.
and can be accessed as either an ide device with dma enabled (for dvd playback) or as a scsi device (for cd burning). It might even have been like this the whole time and I just didn't know about it... But I'm happy now

explain that a little better?

You can enable or disable ide-scsi emulation by passing a kernel parameter at boot time. With lilo, it will be
linux hdc=ide-scsi
for turning it on, and without that parameter for turning it off. You can also edit the lilo.conf or grub.conf accordingly - that's what I had: two entries, one with ide-scsi emulation, one without.

Now, what I did was to boot with ide-scsi OFF. Then the cd-drive is under /dev/ide/etc.etc; the /dev/hdc is just a symlink to this.
When I boot with ide-scsi on, the cd-drive appears under /dev/scsi/etc.etc. and /dev/scd0 (or /dev/sr0 depending on your setup) is a link to that.
I used to think that it is a matter of either/or. Either the cd-drive is under /dev/ide... or it is under /dev/scsi... depending on the boot time options but it is not under both at the same time. And I was looking for a way to change it on the fly w/o rebooting. The link I gave in my first post describes a way to do it but it did not work for me.

It turns out that when I boot with ide-scsi on, the cd-drive is under both
/dev/ide/...
and
/dev/scsi/...
And I have symlinks to both (one is /dev/hdc and the other /dev/scd0). I could also just create them, I suppose. I can activate dma on /dev/hdc by
hdparm -d 1 /dev/hdc
and that makes for smooth dvd playback (/dev/dvd is linked to /dev/hdc). I can use cdrecord because it will use /dev/scd0. All with only one drive - apparently it gets treated as two things internally. Cool