Firmware update planning

What happens if an update fails while running Dell Storage Update Mgr to update a series? Does it roll back to the previous firmware on the failed controller and then stop?

I'm running fw 8.1.4 on 3 PS6210 series and I'm ready to upgrade to 8.1.8 since it's been out for awhile. I'll be trying out DSUM for the first time, and I have 2 groups - 1 with a 6210xs, and another with 2 6210x members. In the past, I've used Grp Mgr and done one at a time, so a fail would only affect one member.

I've only had one failure in the past 10 years, and it was easily resolved, but I'd still like to know as much as I can going in. Thanks.