ZuluIDE V2 rigid HDD write performance in UDMA/33 mode

aperez@oregon:/mnt$ sudo dd if=/dev/zero of=/mnt/testfile bs=1M status=progress oflag=direct count=256
268435456 bytes (268 MB, 256 MiB) copied, 24.847 s, 10.8 MB/s
aperez@oregon:/mnt$ sudo dd if=/dev/zero of=/mnt/testfile bs=512k status=progress oflag=direct count=256
59244544 bytes (59 MB, 56 MiB) copied, 5.91441 s, 10.0 MB/s
aperez@oregon:/mnt$ sudo dd if=/dev/zero of=/mnt/testfile bs=256k status=progress oflag=direct count=256
67108864 bytes (67 MB, 64 MiB) copied, 6.58019 s, 10.2 MB/s
aperez@oregon:/mnt$ sudo dd if=/dev/zero of=/mnt/testfile bs=128k status=progress oflag=direct count=256
33554432 bytes (34 MB, 32 MiB) copied, 3.27403 s, 10.2 MB/s
aperez@oregon:/mnt$ sudo dd if=/dev/zero of=/mnt/testfile bs=64k status=progress oflag=direct count=512
33554432 bytes (34 MB, 32 MiB) copied, 3.39551 s, 9.9 MB/s
aperez@oregon:/mnt$ sudo dd if=/dev/zero of=/mnt/testfile bs=32k status=progress oflag=direct count=1024
33554432 bytes (34 MB, 32 MiB) copied, 3.70979 s, 9.0 MB/s
aperez@oregon:/mnt$ sudo dd if=/dev/zero of=/mnt/testfile bs=16k status=progress oflag=direct count=2048
33554432 bytes (34 MB, 32 MiB) copied, 4.04881 s, 8.3 MB/s
aperez@oregon:/mnt$ sudo dd if=/dev/zero of=/mnt/testfile bs=8k status=progress oflag=direct count=2048
16777216 bytes (17 MB, 16 MiB) copied, 2.40708 s, 7.0 MB/s
aperez@oregon:/mnt$ sudo dd if=/dev/zero of=/mnt/testfile bs=4k status=progress oflag=direct count=4096
16777216 bytes (17 MB, 16 MiB) copied, 2.7041 s, 6.2 MB/s
aperez@oregon:/mnt$ sudo dd if=/dev/zero of=/mnt/testfile bs=2k status=progress oflag=direct count=4096
8388608 bytes (8.4 MB, 8.0 MiB) copied, 2.05258 s, 4.1 MB/s
aperez@oregon:/mnt$ sudo dd if=/dev/zero of=/mnt/testfile bs=1k status=progress oflag=direct count=4096
4194304 bytes (4.2 MB, 4.0 MiB) copied, 1.59854 s, 2.6 MB/s
aperez@oregon:/mnt$ sudo dd if=/dev/zero of=/mnt/testfile bs=512 status=progress oflag=direct count=8196
4196352 bytes (4.2 MB, 4.0 MiB) copied, 2.83212 s, 1.5 MB/s