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alphaniner

Member

From: Ancapistan

Registered: 2010-07-12

Posts: 2,810

[Solved :( ] md5 space optimization of isos

tl;dr - I have a 3.1 GB iso that contains 3.5 GB of data.  I need to figure out how to reproduce this so I can make a modified iso that's still only 3.1 GB.

I have an iso image for a program, and I want to make some changes to the image.  I've done this many times with other similar isos, no problem.  However, when I mount this particular iso, the size of the mounted directory is larger than the iso.  This 'expansion' carries on all the way to the new iso.  Even if I simply make a new iso from the original iso mount dir, the new iso is larger than the original:

$ du ARC_r16.iso
3113520	ARC_r16.iso
$ mount -o loop ARC_r16.iso /mnt/iso0
$ df /mnt/iso0
Filesystem     1K-blocks    Used Available Use% Mounted on
/dev/loop0       3113518 3113518         0 100% /mnt/iso0
$ du -s /mnt/iso0
3563518	/mnt/iso0
$ genisoimage -r -J -l -D -o /mnt/bucket/test.iso -V test /mnt/iso0/
$ du /mnt/bucket/test.iso
3568576	/mnt/bucket/test.iso
$ mount /mnt/bucket/test.iso /mnt/iso1
$ df /mnt/iso1
Filesystem     1K-blocks    Used Available Use% Mounted on
/dev/loop1       3568574 3568574         0 100% /mnt/iso1
$ du -h /mnt/iso1
3563832	/mnt/iso1

So I need to figure out what features account for the size issue, and how I can apply them when I create a new iso.

Last edited by alphaniner (2012-11-12 23:01:24)

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But whether the Constitution really be one thing, or another, this much is certain - that it has either authorized such a government as we have had, or has been powerless to prevent it. In either case, it is unfit to exist.
-Lysander Spooner

Lone_Wolf

Member

From: Netherlands, Europe

Registered: 2005-10-04

Posts: 11,920

Re: [Solved :( ] md5 space optimization of isos

Sounds like this could have to do with the characterics of loop mounting.

What size does the content of the iso have if you COPY the content to a folder ?
How big is  a new iso created from that folder ?

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Disliking systemd intensely, but not satisfied with alternatives so focusing on taming systemd.

(A works at time B)  && (time C > time B ) ≠  (A works at time C)

alphaniner

Member

From: Ancapistan

Registered: 2010-07-12

Posts: 2,810

Re: [Solved :( ] md5 space optimization of isos

Tried that too; essentially the same outcome.  The copied folder was a bit larger IIRC (block size?) but I didn't compare the resulting iso precisely.  I just remember they were of similar size.

I expect it has to do with some sort of symlinking (see for example this).  But like that poster, I was unable to find the proper terminology.  I've yet to comb through the manpages.  Might just go with Imgburn as suggested in that link though.

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But whether the Constitution really be one thing, or another, this much is certain - that it has either authorized such a government as we have had, or has been powerless to prevent it. In either case, it is unfit to exist.
-Lysander Spooner

alphaniner

Member

From: Ancapistan

Registered: 2010-07-12

Posts: 2,810

Re: [Solved :( ] md5 space optimization of isos

From what I can tell, the feature (or more appropriately, function) is 'md5 space optimization' or some such.  AFAICT, only a port of mkisofs called mkisofs-md5 supports this function.  But it seems to be a half-arsed hack as certain basic features are broken:

3a) There is NO Joliet Volume Name even you input "-V VolumeID" in shell.

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But whether the Constitution really be one thing, or another, this much is certain - that it has either authorized such a government as we have had, or has been powerless to prevent it. In either case, it is unfit to exist.
-Lysander Spooner