differences between IDE / VIRTIO / SCSI

Andre Köhler

New Member
Jan 9, 2012
Hattingen, Germany
Hi all,

iam installed Proxmox.

Now i would like create a new VM.

So now the Question is, what Bus/Device should i choose for the first and secound "hard drive".

What are the differences between IDE,VIRTIO,SCSI and what is the best for a Windows Server 2008 guest?

IDE is "normal" or? and the slowest right?
SCSI is "faster" as IDE?! Is a driver need at the guest? (Windows Server 2008)??

And what is VIRTIO?!

Thanks for help

Andre Köhler

New Member
Jan 9, 2012
Hattingen, Germany
First, thanks for that.

Is that so right:

IDE - Slow Write in the Guest System
SCSI - Faster Write(as IDE) in Guest System
VIRTIO - Fastest Write (more that SCSI and IDE) in the Guest System, but only with extra Drivers? (In Guest)
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Reactions: bhatmag1ck


Jan 2, 2012
Basically, install as IDE, add drivers using the above link (basically add a second VIRTIO disk), check you can format the new disk, then go back and set your main disk to be VIRTIO. It's best then to take a snapshot and clone any future VMs from that. Proxmox doesn't appear to have tools to manage that though. You have to start using the command line from what I can tell.

I like to put my backing image in /var/lib/vz/templates/qemu/ and rsync that around my cluster.
Then I can use qemu-img create -b <backing image> -f qcow2 <disk image name> to create the image that will grow as the VM is actually used.

Bear in mind that if you want to change the image though, you'll have to blow away any images based on it, so the best thing to do in that case is to copy the backing image (which is fine as nothing is writing it) to a new file.
create a new image backed to the new file, make your changes and then sync your changes back to the backing image. (all with qemu-img) Then you can start to base new machines on this new baseline. One word of warning, you can't upgrade your old machines to the new baseline simply by changing the backing file. It probably won't work and may cause instability and crashing even. This works best with a DHCP based system as manually configuring the IP each time is a bit of a chore. Don't join your baseline to a domain, leave that until your machine has the correct name and IP.

*I am not really a windows admin, I'm just managing some windows boxes and applications so this is expedient rather than best practice.



Active Member
Mar 30, 2012
My question is sort of related to this, so here goes.

We have a 30 vm (nearly all linux) setup with all of them IDE drives.
These machines are always switched on and working (builds).
They were created quite some time back.

I was thinking of converting the drives to SCSI (or Virtio) to gain disk speed inside the vms.

From the above posts I understand that I should definitely see a performance increase in the disk throughput inside the vm.

My question is:
How will changing the IDE to SCSI (or VIRTIO) affect CPU usage of the base ProxMox host?
Will the CPU usage of the base ProxMox increase?

Shantanu Gadgil


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