Disk optimization

...

Shutdown the windows guest.
Open flexvdi dashboard, click on "modify" over the guest, and add a new disk image. Use a size of 5 MB to make the operation fast. Mark the newly created drive as "virtio", instead of the default "ide" in the table of disks. Click "Finish" in the last step. This virtual disk will only be briefly needed during installation to make windows install virtio driver. Do not change the type of the other disks yet.
Now the virtual machine has a new virtio drive, but windows still can´t access it.

Install

...

First you have to make sure that your machine has a virtual CD drive. Go to flexVDI Dashboard, find the guest you are working on and click on the storage tab. Under "Media images" you will see a list of the "virtual CD drives" that the machine contains. If there isn't any entry, you will have to stop the machine before changing its hardware. Once it is stopped, click on "Add Image", and Save your changes.
Start the guest again.
In flexVDI Dashboard, find the guest you are working on and click on the storage tab. Under "Media images" you will see a list of the "virtual DVD drives" that the machine contains. Under "Media Images", you can change the "virtual CD" without stopping the virtual machine. Select the value "Internal MS" in the Media storage drop down, and "guest-tools" in the "File" input. Then click on the button "Change media". This will insert a virtual CD in the guest.
Now open Windows Explorer in the guest. Open the disk labeled "flexVDI Guest Toolsv3.x.x Setup ", and double click on flexvdi-guest-tools-3.x.x".
If you agree to the license terms, click "Agree" and proceed with the installation. The first screen lets you choose the components to install. During the installation you will be prompted to confirm the installation of several drivers.
Now open MS-Windows disk management (In windows 10, right click on "This PC", then click on "manage", and then "disk management"). The temporary disk should appear here.

...