You need a special type of DVD Media for pseries to make the backup on.
I remember I was facing the same issue, until i researched online...
This media is called DVD-RAM. Try with this media and it will 100% work.
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Creating a root volume group backup on DVD-RAM with Universal Disk ...
Enter the name of the
DVD-
RAM device. If you are creating a
mksysb image, select yes or no for the
mksysb creation options. The options are as follows:
...
publib.boulder.
ibm.com/...
ibm.../creating_backup_
dvdram_udf.htm -
Cached
mkdvd Command
Use this flag if creating a
mksysb DVD that you will not boot.
...
publib.boulder.
ibm.com/infocenter/aix/v6r1/topic/com.
ibm.../mk
dvd.htm
mkcd Command
If you do not specify the -m flag, the mkcd command calls
mksysb.
...
publib.boulder.
ibm.com/infocenter/aix/v6r1/topic/com.
ibm.../mkcd.htm
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