4 Disk Raid 5 Array on a P420i/1GB Controller.
Now based on how it's always worked, and HP's own documentation how you would do an online migration to RAID 10 is add some spindles. Go into SSA, add the spindles to the ARRAY so the ARRAY has free space to do the migration. You DON'T touch the Logical Drive.
You can confirm this process here. http://h20565.www2.hp.com/hpsc/doc/public/display?ac.admitted=1415232583597.876444892.492883150&docId=emr_na-c04250626
Now what actually happens with SSA vs ACU? I'll tell you. You add the disks to the ARRAY and HP takes it upon themself to assume you want to expand the LOGICAL DRIVE and does so automatically. Now you're completed F'd. It expands the RAID 5 volume using the new disks and now you have a massive Array you didn't want with no free spindles for the RAID migration and no way to get them back, as you can't shrink Logical Drives.
I'm absolutely fuming. HP once again makes me look like an idiot to my client.
I believe I've exhausted all options, but if anyone has some insight it would be much appreciated. Words can't describe my level of frustration.