Re: writing cdhdtape to CD

["Michael L. Hitch" <mhitch%lightning.msu.montana.edu@localhost>]

On Mon, 1 Jun 2009, Michael L. Hitch wrote:

>  I think the cdhdtape image was used before the iso images were generally 
> available, and I suspect that they haven't been tested in quite a while and 
> the install documentation likely needs some updating depending upon whether 
> the cdhdtape image is no longer valid or if it just needs some fixing.

  I think I may have figured out what is happening.  The ustarfs read 
routine reads the input media in 18K chunks (designed for floppy disks), 
and as best I can tell, will get an error if the media has less than 18K 
at the end.  Reading from the disk will work, since there will be garbage 
blocks after the image that will read fine, but on a CD, an error will 
occur trying to read the last part of the image.

  I think this used to work in the past when the alpha was generating the 
image file with alpha-specific code.  The image was a fixed size and would 
have sufficient spare space at the end of the image so that the ustarfs 
read would encounter the end of the data before it hit the end of the 
actual image written to the CD.  The common code, shared by many other 
ports, appears to write the last 'floppy' image with just the amount of 
data to terminate the tar file, but would generate an image size that 
wasn't necessarily a multiple of 18K.  This would probably cause the 
problem you are seeing.

  A quick test would be to pad the cdhdtape image to a multiple of 18K, 
burn that adjusted image, and see if it works:

dd if=cdhdtape of=/tmp/cdhdtape bs=18k conv=sync

  The /tmp/cdhdtape image might work better.  If I get a chance to waste 
another CD and can reboot one of my alphas, I could try this.  [I've 
already tried a couple of different cdhdtape images, and had some trouble 
getting the alpha back running properly.]

  The Makefile.tarfloppy shell script used to create image has the option 
of padding the created image file to the specified size of the 'floppy' 
image (18K for real floppies, and 5MB for the alpha cdhdtape), so if this 
is the actual problem, it will be easy to cure it.


--
Michael L. Hitch                        mhitch%montana.edu@localhost
Computer Consultant
Information Technology Center
Montana State University        Bozeman, MT     USA