That's a little strange, were you downloading directly to the array or was cache also using the HBA? Were normal array writes still OK, just the apps downloads were slow?
P.S.
Aug 17 11:42:50 Tower kernel: REISERFS warning: read_super_block: reiserfs filesystem is deprecated and scheduled to be removed from the kernel in 2025
You need to convert all reiser disks to xfs, also note that reiser is known to under perform with full disks, but it should be the same with either controller.
Note that even if the problem is fixed the 1st check might find errors, from previous runs, after those are fixed no more should be found on future runs.
-stop array, click on the empty disk, change fs to reiserfs
-start array, format disk
-stop array, click on the disk, change fs back to xfs
-start array, format disk