Performance for passthrough discs

[pma66271]

Hi community,

I am using PME 7.0-13 with four discs (1 SSD, 3 HDD) that are passed through to a Windows 2012 Server VM.
The discs are encrypted with veracrypt from inside Windows.

If I copy a file (~10 GB) from the SDD to any of the HDD, the transfer rate goes dramatically down after ~4 GB. Starting with ~200 GB/Sec.
This behavior can be reproduced with any other file > 4 GB.

Before I switched to PME I was running same Windows on bare metal and never faced this issue.

Can it be solved by configuration adjustments or do I have to live with it?

 

[pma66271]

Push

 

[Dunuin]

I guess what you are seeing is just the caching. Windows will write the first 4GB of that file into RAM so it looks fast and then the RAM is full, it will write directly to the disk and you see the acutal disk performance which can't handle more than that 16,3 MB/s. I guess you used "qm set" to passthrough the disks? Did you added them am SCSI and selected "Virtio SCSI" or "virtio SCSI single" as the storage controller for that VM? If you you should try that. Virtio SCSI is way faster than for example IDE. Also make sure you set the AES-NI flag for your VMs CPU so VeraCrypt can make use the AES-NI instructions of your CPU for faster encryption.

 

[bbbesb]

Hi guys,
I know it's an older thread, but I do confirm that that issues in combination with VeraCrypt still exists, resulting in writing speeds at around 30MB/s throughout (tested on SSDs and Windows Server 2022)

Things I tried:
- several Proxmox versions from old 7.x branch to the latest 8.1.4 and its respective virtio-drivers.
- different HW
- using container instead of full disk (both on the system disk and on the passed through drive)
- passing through the drive with different Bus/Device types (virtio, sata, scsi)
- playing around with different mounting types in VeraCrypt
- VeraCrypt installed vs. portable

The HW(s) mentioned work(ed) perfectly fine in conjunction with ESXi and/or on bare metal

What do you think the is the core issue?
I'd really appreciate if someone could have a look.

Thanks in advance