We've just done an 8.1 to 8.2.4 upgrade on a FAS3220
If it helps, we were advised by support to go to the latest 8.1.x first, BEFORE moving to 8.2.x to reduce the likelihood of upgrade issues. As such we went first from 8.1 to 8.1.4P9, and then 8.1.4P9 to 8.2.4
NOTE as of 8.2.x shelf and disk firmware is now part of the firmware upgrade, whereas prior to 8.2.x you had to download it separately.
Also for info, 8.2.4P2 is now out, although as above, at 2 days old, it is too new to be the recommended upgrade option as yet.