Correct Disk Speed in VM?

[pixelwave]

I am a bit confused I have installed a Windows 11 Pro virtual machine on my Proxmox Server. That virtual machine is stored on a mirrored ZFS pool (2x WD Red SN700 NVMe) and the NVMe's are connected to the onboard NVMe slots of the "ASRock Rack X470D4U" (PCIe 3.0 x2, PCIe 2.0 x4).

The theoretical disk speed should reach a maximum of 2.000 MB/s read/write. Yet when running CrystalDisk I get those results:

 

[Dunuin]

CrystalDiskMark ia only doing async reads/writes and these will be cached by Windows in RAM, maybe by KVM in the hosts RAM (writeback/writethrough) and by ZFSs ARC in the Hosts RAM. So you are basically benchmarking your RAM with CrystalDiskMark.

 

[pixelwave]

That what I thought ... maybe something connected to RAM/ZFS.

But the write speed should be actual speed of the NVMe drives? It seems more realistic ..

 

[Dunuin]

That what I thought ... maybe something connected to RAM/ZFS.

But the write speed should be actual speed of the NVMe drives? It seems more realistic ..

Its also only RAM...If you want to see the real write performance you need to use fio with sync writes and write long enough that the SSDs DRAM + SLC cache get fully filled up. The real write performance once the caches are full would probably be a few hundred MB/s only.