[syslinux] isohybrid and ISO images whose size is not a multiple of 2048 bytes vs. VirtualBox

[Thomas Schmitt]

Hi,

Ady wrote:
> I fear we would get slightly off-topic.

Yep. Since the TAILS ISO is supposed to not grow over 2 GiB
for now, it seems best to just use -h 128 -s 32 in order to
stay near to traditions.


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Summary:

The alignment to cylinder size is a core feature of isohybrid.
If -h multiplied by -s is not divisible by 4, then ISO image
files may emerge from isohybrid which are not aligned to
2048 bytes. This is bad if the file shall be used as
virtual DVD-ROM.

The waste caused by a particular cylinder size depends on
the size of the ISO input image.
It is well possible to automatically determine a cylinder size
for minimum waste while keeping it divisible by 2048.
But it would probably produce non-traditional sizes.
(Whatever the importance of a traditional size is.)

It might be beneficial for the community if everybody tests
-h 252 -s 63 whether it suits as replacement of the advise
to use -h 255 -s 63 with large ISOs.

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Have a nice day :)

Thomas