[TriLUG] dd limit on disks?

[Joseph Mack NA3T]

I do windows backup by dd'ing the whole disk to my linux 
machine (after defragmenting and filling the disk with 
zeroes). I check that I've got something sensible by 
mounting with -o loop, I then gzip the image. This has 
worked fine so far as the windows disks have been small 
(6G). If a disk crashes I have to restore to a disk of the 
same geometry. I find this works to clone a 10G disk to 
another bigger (40G) disk (maybe I've just been lucky).

I just installed WinXP on a 30G disk and then tried to back 
it up with dd. I recovered only about 6G (6495068160bytes = 
63 sectors * 3 surfaces * 16 heads * 5(I don't know what) * 
839 (cylinders?) * 512). (total cylinders is 16,383: 
16383/839=19 if that helps). Thinking there was something 
wrong with the disk, I did it again with the same result. 
Picking another 30G disk (same type) with linux on it, I got 
the same result. I seem to have got about 20% of the disk.

ulimit is unlimited.

I have some other random sized disks I could try. Since dd 
doesn't care about the filesystem, I'm only copying bits. 
Anyone know why I can't dd the whole disk, no matter what's 
on it? Google didn't find any problems.

Thanks Joe

-- 
Joseph Mack NA3T EME(B,D), FM05lw North Carolina
jmack (at) wm7d (dot) net - azimuthal equidistant map
generator at http://www.wm7d.net/azproj.shtml
Homepage http://www.austintek.com/ It's GNU/Linux!