From my experience DP A.08.12 is quite stable now. Just make sure you apply the patch bundle 8.12 right after the actual software upgrade. Even for A.08.1x the upgrade is as simple as run omnisetup.sh. Just stick to the Installation and Upgrade guide and you should be fine.
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I've downloaded the software, unzipped it, untarred it, read the install/upgrade instructions several times and finally was ready to run omnisetup.sh on my existing 6.20 cell manager/installation server/client, which is an rx3600 running HP-UX 11.23. It tells me "platform not supported" and quits (see below). What now???
Data Protector version A.06.20 found Cell Manager detected... Installation Server detected... Client detected, installed packets: cc javagui da ma docs
Do you wish to start AutoPass installation? (Y/n) n AutoPass installation skipped.
Installing Data Protector A.07.00 Cell Manager and Installation Server...
Cell Manager for hp/sia64/hp-ux-11 platform is not supported. Exiting...