[Pkg-libburnia-devel] Large size penalty from -isohybrid-mbr and -partition_offset 16?

[George Danchev]

On Wednesday, June 15, 2011 04:53:46 PM Thomas Schmitt wrote:
> Hi,

Hi,

> > The 1MB penalty for -isohybrid-mbr is larger than I expected,
> 
> Alignment to full cylinder size was prescribed by hpa at SYSLINUX
> mailing list, when he defined the constraints of isohybrid.
> 
> The alignment was not performed by mistake with the earlier
> point releases of Debian 6. The only negative effect was that
> fdisk -lu complained about differing "physical" and "logical"
> cylinder sizes.
> 
> You may disable this by xorriso -as mkisofs option
>   -partition_cyl_align  off
> 
> > but the
> > last size is particularly weird.  Why is there a 3MB size penalty for
> > having a 32KB partition offset?
> 
> The partition offset creates a second directory tree, which can be
> mounted as /dev/sdX1. Its size depends on the number of files in
> the image.

and two super blocks of 512 are also created, but their addition is negligible 
AFAIUI.

> ISOLINUX works with the tree for /dev/sdX, but at some point of
> the boot process, the other tree might get into effect.
> 
> See also http://libburnia-project.org/wiki/PartitionOffset
> 
> Option -J caused another pair of directory trees with Joliet names.
> 
> You can get an estimation of the size of metadata by inquiring the
> start address of the first data file.
> The run:
>   xorriso -indev oneiric-server-i386.raw \
>           -find / -sort_lba -exec report_lba -- 2>/dev/null | head -2
> 
> will report something like
>   Report layout: xt , Startlba ,   Blocks , Filesize , ISO image path
>   File data lba:  0 ,       67 ,      370 ,   757248 , ...some.path...
> which tells that the directory trees end before block 67 * 2 kB.
> 
> ------------------------------------------------------------------------
> 
> 
> I am a bit puzzled by the fact that xorriso -isohybrid-mbr isohdpfx.bin
> yields a size of 658 MB + 300 kB.
> 300 kB is the usual default padding, but it should be counted as part
> of the image.

He might had well skipped the -jigdo and -as mkisofs part with the subsequent 
runs, in which case padding (default 300kB) is not counted as part of the 
image size. My hypothesis only.

-- 
pub 4096R/0E4BD0AB <people.fccf.net/danchev/key pgp.mit.edu>