Here's my list of what seems to break, or gives hard-to-trace-down errors:
- There's a new -econfig option sent by version 9 cell managers which means that an earlier version of the Exchange 2010 agent quits badly (which the session manager reports as insufficient priviledges on CreateProcess). Note that you'll probably hit the Client named "MS Exchange 2010 Server" error first.
- Some SQL backups work, some don't. I can't see what it is that's different between them, though.
- Filesystem backups won't break, but I have noticed that very old agents (e.g. version 5) will give a warning about an unknown option if you have a cell manager that understands enhanced incremental backups.
But other than that, I've been reasonably successful upgrading the cell manager first, letting a few backups run to make sure that everything is working, and then slowly upgrading a few clients at a time. There doesn't seem to be a need for flag days where every single client gets upgraded at the same time.
Greg Baker is an independent consultant who happens to do a lot of work on HP DataProtector. He is the author of the only published book on HP Data Protector (http://x.ifost.org.au/dp-book). He works with HP and HP partner companies to solve the hardest big-data problems (especially around backup). See more at IFOST's DataProtector pages at http://www.ifost.org.au/dataprotector