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Old 11-24-2010, 06:05 PM   #1
stf92
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Mkisofs: second session vs higher level session.


From mkisofs man page, 2.01:
Quote:
-C last_sess_start,next_sess_start
This option is needed when mkisofs is used to create a CDextra
or the image of a second session or a higher level session for a
multi session disk. The option -C takes a pair of two numbers
separated by a comma. The first number is the sector number of
the first sector in the last session of the disk that should be
appended to. The second number is the starting sector number of
the new session. The expected pair of numbers may be retrieved
by calling cdrecord -msinfo ... If the -C option is used in
conjunction with the -M option, mkisofs will create a filesystem
image that is intended to be a continuation of the previous ses-
sion. If the -C option is used without the -M option, mkisofs
will create a filesystem image that is intended to be used for a
second session on a CDextra. This is a multi session CD that
holds audio data in the first session and a ISO9660 filesystem
in the second session.
What is the difference between a second session and a higher level one? Thanks in advance.

Last edited by stf92; 11-24-2010 at 06:06 PM.
 
Old 11-24-2010, 06:41 PM   #2
w1k0
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There is no difference -- all of them are later than the first session.

For example you'd like to burn the contents of the current directory and prepare CD-ROM disk for the burning of the future sessions. In such case you can prepare image.iso file using the command:

Code:
mkisofs -r -J -D -o image.iso .
and burn it in multisession mode using the command:

Code:
cdrecord -v dev=/dev/cdrw -multi speed=12 image.iso
After that you could burn the contents of the other directory on the same disk. In such case you can prepare image.iso file with the command:

Code:
mkisofs -r -J -D -C `cdrecord -msinfo dev=/dev/cdrw` -M /dev/cdrw -o image.iso .
and burn it in multisession mode using the same command as before:

Code:
cdrecord -v dev=/dev/cdrw -multi speed=12 image.iso
The resulting CD-ROM disk has data stored in both burned directories. If some file burned during the consecutive session has the same name as the file burned previously the newer file overwrites the older one.

To close CD-ROM disk write the closing session with the command:

Code:
cdrecord -v dev=/dev/cdrw speed=12 image.iso
 
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Old 11-24-2010, 07:55 PM   #3
stf92
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Quote:
Originally Posted by w1k0 View Post
The resulting CD-ROM disk has data stored in both burned directories. If some file burned during the consecutive session has the same name as the file burned previously the newer file overwrites the older one.
OK, and thanks a lot. But is the space ocupied in that disk by both of the directories the same as the sum of the space occupied by the first on some disk and the second burned on some other disk?
 
Old 11-25-2010, 08:45 AM   #4
w1k0
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Assuming you change the contents of some file and you burn it for a few times on the same CD-ROM disk each consecutive burning occupies more of the disk space because all previous burned sessions persist on that disk. As for different files burned in a few sessions I suppose they occupy slightly more CD-ROM disk space than the same files burned in one session.

I suggest you to perform simple experiment. Collect ten files of about 500 MB in total and burn them in one session on the first CD-ROM. Then burn the same files in ten sessions on the second CD-ROM. Use the CD-ROM disks by the same manufacturer and of the same type in both cases. After that compare the sizes of both CD-ROM disks.

Finally publish the results of that test here for other people knowledge.
 
Old 11-25-2010, 09:29 AM   #5
stf92
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Kind of you to have replied. I'll put to work on what you've suggested. But, I anticipate there will be a difference within 5% in used CD-ROM space. The alternative would be like this (example): file A= 100M, file B=150M. First session: I record file A. Second session: I record file B. Now, used space on CD-ROM= 100M from first session + (100M + 150M) from second session. That is, file A has been written twice on the disk, consecutively. And my question was: is this the case? Regards.
 
Old 11-25-2010, 10:07 PM   #6
w1k0
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I tried to burn two sessions on one CD-ROM disk but I failed for the three times. My three CD-ROM drives refused to work. I'm too tired now to test that throughout. I still have a few empty CD-ROM disks so maybe I'll try to write them tomorrow.

As for your question I suppose you burned during the second session both A and B files.
 
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Old 11-26-2010, 02:58 AM   #7
stf92
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Quote:
Originally Posted by w1k0 View Post

As for your question I suppose you burned during the second session both A and B files.
No, I only burned file B duriong the second session. And this answers my question in the negative. Ie, there is no redundancy and file B is, on the final disk, only figuring once. Thanks a lot.
 
  


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