Use /dev/rdiskX instead of /dev/diskX for physical hard disk to make disk IO 10x faster.

Description
Currently, when we add a physical hard disk to VM, Parallels opens /dev/diskX by default.
I can observe this behavior by inspecting open files list in Activity Monitor. It shows that the VM process opens /dev/disk4 in my case.
However, the performance of /dev/diskX is quite poor according to https://superuser.com/questions/631...out-20-times-faster-than-dev-disk-in-mac-os-x
You can easily see the significant performance difference by using "dd" command to write on /dev/rdiskX and /dev/diskX respectively.
So I suggest to use /dev/rdiskX by default when using physical hard disk.

Test case
Version: Parallels Desktop Pro for Mac 15
Host: Macbook Pro 2019 high profile model, macOS 10.14.6
Guest: Windows 10 1903, with parallels guest tools installed.

I have an external NVMe enclosure with USB Type-C 3.1 gen 2 connector. The SSD inside the enclosure is Samsung 960 pro, which included a preinstalled Windows 10 using Windows to Go.
Then I created the VM, choosing this external physical drive as boot drive. The guest OS booted as expected, everything works well.
So I perform a disk speed test using "AS SSD Benchmark" software in guest OS. It shows the sequential read is 100-150MB/s, write is 120MB+/s, which is unusual since the normal sequential read/write speed of this external NVMe drive over a USB 3.1 port is around 900MB+/s and 700MB/s.

If I boot the disk on a linux host with QEMU-KVM(Guest VirtIO drivers installed), the sequential IO benchmark result inside guest OS is around 600-700MB/s read and 400-500MB/s write. I haven't tested it on macOS host with QEMU.

I tried to change the disk location option in advanced settings to NVME/SCSI/SATA, but it doesn't seem to make a noticeable impact on IO speed inside the guest, so I inspect the opened files list of the VM process via Activity Monitor, and it confirms that Parallels VM opens /dev/disk4.
/dev/disk4 is the external NVMe drive mentioned above.

Maybe the poor disk IO performance inside guest is caused by using /dev/diskX? How do I change it to /dev/rdiskX manually? I didn't see any setting related to it in config.pvs file.

 

I also tried to set <Passthrough>1</Passthrough> in <Hdd> section in config.pvs file, but it doesn't help.