[syslinux] MEMDISK issue with OptiPlex GX280,620

Shao Miller Shao.Miller at yrdsb.edu.on.ca
Wed Dec 8 18:46:58 PST 2010

On 12/8/2010 17:30, Jason Vasquez wrote:
> Splendid trick using dd to help better compress an image. I did not 
> know that was possible. Thank you for sharing.

Glad you enjoy it.

> More information now to share about my MEMDISK issue for possible 
> reference. I created an ISO image of my test disc that contains the 
> PC-DOS/Ghost disk image. I then remastered the test CD to include the 
> ISO image

Just to confirm: You boot an optical disc which then boots MEMDISK with 
an .ISO, which then boots MEMDISK with the HDD DOS utility image?

   BIOS -> CD/DVD -> ISOLINUX (version unknown) -> MEMDISK 4.03 -> 
test.iso -> ISOLINUX? (version unknown) -> MEMDISK (version unknown) -> 
HDD image

Something like that?

> Using SYSLINUX 4.03's MEMDISK to boot the ISO image file surprisingly 
> allowed for the Ghost environment to see the GX280's SATA drive. That 
> is, no "We lost the last drive in our class of drives" occurred using 
> this approach -- booting an ISO containing the HDD image, unlike 
> booting the HDD image directly. Doubly odd, no?

Actually, I'm not all that surprised.  That is why I asked how you were 
booting it.  It could be the case that your BIOS misbehaves, depending 
on the boot medium choice.  MEMDISK uses the BIOS INTerrupt 0x13 service 
in its disk probing strategy.  If your test resembles the setup outlined 
above, there is a MEMDISK INT 0x13 hook in place before the second 
MEMDISK disk probing.  That means that when the second MEMDISK probes 
drives, it's actually using the first MEMDISK's INT 0x13, which could 
very well yield different results than using the BIOS' INT 0x13.

Another advantage to using a "superfloppy" image _might_ be: masking 
your issue. :)  With a superfloppy image, you'd specify "floppy" to the 
MEMDISK kernel, and we'd probe drives starting at 0x00 instead of 0x80, 
which was returning "Yes, there's a drive there" for every drive >= 
0x80.  It would be interesting to find out if MEMDISKing a floppy would 
do the same.

So to confirm again: The failure scenario is: Which version of PXELINUX 
and which version of MEMDISK?

Also: Could you please try the 'nopass' directive and report if there's 
any difference?

- Shao Miller

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