Best Option For Passing HDD to VM

[zuluromeo]

Good morning,

I have a Mediasonic 8 bay Probox with 8 HDDs in it. For some reason, when I originally setup my VM, I followed the directions here and passed each disk separately. But now that I am trying to troubleshoot why they are not spinning down, I realized that they show up in the VM as QEMU HARDDISK.

So now I am wondering why I did not just pass through the USB port instead.

Any advice on which is better and why I should pass disks separately instead of the port? I plan on always having all eight disks being used in the same VM.

Thanks!

 

[Dunuin]

If you use "qm set" to passthrough your individual disk they are still virtualized so you get virtualization overhead, can't use all the features (like SMART, 512B instead of 4K blocksize and so on) because of the additional abstraction layer and your VM can only see the virtual disks (QEMU HARDDISK).

USB passthrough on the other hand is slow and not very reliable because it is fully emulated.

If you want your VM to be able to directly and physically access the disks you need to use PCI passthrough. You can either get a PCIe USB card or a PCIe HBA card (for SATA/SAS), attach your drives to it and then passthrough the complete USB card/HBA to your VM. That way that USB controller/HBA is an actual part of your VM and the VM can physically access it and everything attached to it will automatically be part of your VM and the VM can use the real drives.

 

[zuluromeo]

Thank you for the information. Unfortunately, I am running this on a Protectli Vault and PCI cards are not supported.

You say that ”qm set” has virtualization overhead and that USB passthrough slower because of emulation. Which would be faster? Since they are slow spin HDDs, I am not exactly setting any speed records.

Thanks!

 

[Dunuin]

Then I would go with "qm set" and SCSI. Then its atleast paravirtualized. And if you don't just want the HDDs to be a backup storage its discussable if a spindown makes sense at all. Yes, if will save power but on the other hand it might be possible (no common consent studies about it as far as I know) that your HDDs will die sooner. With spindown / head parking you get more thermal changes and more stress for the mechanical parts compared to just let them spinning.