download affects all the disks, so you won't need to redownload the kernel (unless, of course, you're upgrading the kernel at the same time).
In theory that's true, but a couple months back I ran into a bug in 5.0R1 on a 630 after destroying a volume with 22 disks (on a 24 disk filer). The filer wouldn't boot off disk until I booted off floppy and ran download. I think the vol destroy command uses a "hardware erase disk" function. If you erase the vast majority of your disks, you may have trouble the next time you reboot unless you download. The problem was easily repeatable.
I reported the bug to netapp unofficially (since the box was a eval), but never heard if they tracked down the problem. I'd suggest doing the download after the vol destroy/vol create operation even though in theory it's not necessary.
It'd be nice to know if Netapp tracked this one down.
Darrell Root rootd@nas.nasa.gov