Help with CHS / geometry

[vom513 <vom513%gmail.com@localhost>]

Hello all,

So I’m messing with a ZuluSCSI SD to SCSI emulator card.  The card itself is wonderful, however I’m really struggling with disk geometries, as well as what size to make the “blank” disk image.

Here is an example from someone’s dmesg they posted.  This is an IBM drive they have, here is the pertinent line:

sd0: 8715 MB, 8387 cyl, 10 head, 212 sec, 512 bytes/sect x 17850000 sectors

This is very similar to what I’m trying to do.

If I plug those values into an online disk geometry calculator (ex: https://www.deathwombat.com/diskgeometry.html) - it tells me the total bytes of the drive is 9103585280.

However, if I do the math presented in the dmesg I found, 512 x 17850000 is 9139200000.

So when I make a “blank” drive image to put on my SD card, which of those values should I be using ?

Either:

dd if=/dev/zero of=HD30_512-8.5gb-BLANK.hda bs=512 count=17850000

OR

dd if=/dev/zero of=HD30_512-8.5gb-BLANK.hda bs=512 count=17780440

I know this isn’t technically a sparc question per say…  but I figured folks here would know the magic numbers to make it all happy :)

Thanks in advance.