Solaris

I really see no problem at all using growfs on a hardware raid. if you already see the free space on the volume then go ahead enlarge your slice and use growfs.

What the rest is referring to I think is when you upgrade each disk one by one. Then indeed, you will not see the extra space in your volume and will not be able to make your slices bigger.

Can I enlarge a slice on-line without loosing the data? I don't think so.
What do you mean by upgrade then? I think your assumption is wrong. Did you try it yourself first?

incredible - i wouldn't growfs on a hardware raid on a production box with critical/important data. i would set up a test case first IF you can. my feeling is it could work but who knows how the raid controller will handle this situation especially since you target the raw disk. i could probably give it a test in one of my servers with hp smart array p400 raid controller.

This is on a client's system, thats why Im hesitant to provide any confirmation to them

Incredible, am curious to know if/how you solved this issue.

Not yet, client is putting this activity on hold for now