Forum: EasyBoot
Topic: ISO menu - Optimize button destructive?
started by: wixfigur
Posted by wixfigur on Oct. 30 2005,15:51
Hi - one little question: is the optimize button in iso menu destructive to my disc1 folder ( means make any changes in this folder ), or does it only change the iso file? I am a little bit afraid that it would mess up my different i386 folders. maybe i want to make changes in i386 folders after I made an iso, so maybe its not possible anymore.

thx wixfigur
Posted by eureka on Oct. 30 2005,16:19
To wixfigur

Yes, I think you are on the right track there wixfigur. If “Optimize” used, then it’s nearly impossible to change structure in ISO-file. Some parts may work but some parts not.

You can see it as files are “cross-linked” (one/same file used to several parts in ISO-file). Changes to such file, have heavy impact to other parts in ISO-file, because it’s using same file.

I have tested to make changes (using WinIso) in ISO-files, made with “Optimize” activated, and every time there’s problems.

eureka
Posted by mionica on Nov. 04 2005,18:45
@eureka:
ISO layout optimizations works very well, as long as you do your editing with UltraISO.

@wixfigur:
Optimization does nothing to your files, it only affects the layout of the generated ISO file - that is, files apperaring in more places are stored only once. "Crosslinked" indeed, as eureka mentioned - however, this is not important unless you need to edit the file directly, later on.

If you really need to edit such a file, UltraISO does work (I can remember a lot of former -now fixed- bugs, but I don't remember any to have been related to layout optimization). I did install once WinISO, and found it not to be to my liking - I removed it in about 20 minutes.

And, of course, there'se a 100% foolproof method to editing optimized ISO's: extract all the contents, change what you will, and lastly rebuild the image from scratch (just don't forget to save/restore the boot file; in extremely rare cases, you also need to preserve the CD label - for instance, for the Paragon Recovery CDs). There is a 0% (zero percent) chance to get things mixed up this way unless you need HFS, HFS+ or RockRidge. Nota bene. If you're not dealing with a Macintosh or Linux disk, you won't ever care about these. This method however takes longer than direct editing.

@all
The concept of (ISO) disk layout optimization was first introduced by Microsoft, on a Windows 2000 disk distributed through MSDN; this disk - probably the first multiboot CD ever made - had Windows 2000 Professional, Server and Advanced Server all on the same disk. Later on, the major CD mastering tools (Microsoft's CDIMAGE and GNU's MKISOFS) also introduced the concept of layout optimization.

To better understand layout optimization, take the following example: a multi-boot disk containing XP RTM, XP SP1 and XP SP2. These would take over 1.5Gb together, and more than 1.2 Gb with the non-european language support removed.
However, most of the files in RTM were not altered by neither SP1 nor SP2, and several files specific to SP1 were not altered in SP2. Therefore, there is no reason that one file which exists in three places be stored three times - once is enough, if only the file appears in all the required folders. This is what optimization does - it checks for duplicates, writes the directory entries as if nothing happened, but all the files with the same content share the same data.
By removing the non-european language support from the three aforementioned Windows versions, and by using disk layout optimization, I was able to fit all the three Windows versions on the same CD (not DVD).
Posted by eureka on Nov. 05 2005,02:17
To mionica

Quote: ”And, of course, there'se a 100% foolproof method to editing optimized ISO's: extract all the contents, change what you will, and lastly rebuild the image from scratch”. I always use this method. As you pointed out, this is the 100% safe method.

Anyway, interesting notes about UltraIso.

Regards eureka
Posted by mionica on Nov. 22 2005,20:33
@eureka

A final note.

The exact concept used by CDIMAGE/MKISOFS/UltraISO et co. - is a feature of most of the file systems.

In all versions of UNIX filesystems I know of (including the Linux EXT2/EXT3), as well as in the case of the NT filesystem (NTFS, 1.2 to 3.1), support for such "crosslinking" is implemented right into the core. UNIX/Linux users have the command ln link file, and NT/2000/XP/2003 users have the command fsutil hardlink create link file, which actually create a mirror, named link, of the file file. Any changes to the newly-created "link" actually occur to "both" files (actually, there's only one file, with multiple dierctory entries).

Of course, this feature can lead to sore mistakes when used without care. However, the very fact that this kind of optimization is embedded in such serious file systems as EXT3 and NTFS, makes it logical to conclude that it is quite normal to take advantage of it, whenever at hand.

As such, the reason for occuring errors is not the concept of "mirror files" in itself, but rather the poor implementation of it. Editing an optimized ISO image with tools unable to handle crosslinks accordingly is just as safe as writing to an NTFS partition using a tool that doesn't balance the filesystem trees (B*Trees, if I recall correctly). At best, the NTFS would get slower; at worse, coorupted; at worst, destroyed.

A final note. Of all the common filesystems, only with UDF (in read/write mode; not the one used on DVDs) and with the FAT family (FAT12, FAT16, FAT32) crosslinking may lead to serious (unpredictable, that is) errors. And this happens because these FS's do not separate the file entity from the directory entry entity referring to it. Any serious FS makes no such confusion. HPFS, EXTx, NTFS never confuse a file with a reference to it; also, all readonly filesystems (UDF on DVD-ROMs - but not on DVD-RAMs; ISO9660; Joliet; etc) are fit for such crosslinking without endangering at all the contained data.

I hope this was not too boring a post. I just felt the need to pinpoint the actual problem; that is, the fact that the problem with optimization does not reside in the concept itself, but rather in the poor coding of some tools. And, as I already mentioned, UltraISO is really safe - at least, when the "Recompile when saving directly" option is checked.