As I don't have enough internal storage space on my MacBook Pro, I used to store my Parallels VMs on an external 500 GB HDD connected via Firewire 800. However, that drive eventually died, and I replaced it with a 3 TB Western Digital NAS.

Now, my Parallels VMs run extremely slowly. Actually, to be more specific – they seem to run at normal speed, but take forever to respond to UI inputs (e.g., when I click a button, there's a 30 to 60-second wait before it responds. But once it does, the UI updates smoothly).

Is there anything I can do to speed up the UI responsiveness, or is this just a side effect of running the VMs off of the NAS?

I run three different Windows VMs (two Windows 7, one Windows 8), and they're all equally slow, so it's not an issue with just one VM. I also haven't changed any settings or anything else other than moving them from the old FW800 HDD to the NAS.

  • What if anything it says in the Console.
    – Ruskes
    Jul 30, 2014 at 18:51

1 Answer 1


All three of your VMs are stored on your NAS, correct? I am not surprised that they are all slow. You are streaming tons of data over a network and expecting it to work as if it were being used locally.

Virtual machines perform a lot of disk IO. Using network storage for VHD files and other resources that are used by your VMs is not really a great idea if you need responsiveness. A lot of software has been developed to try and solve the issue of streaming VMs over a network.

You may want to look into the many VDI solutions that are available if you really want to continue using your VMs over a network. Just a thought.

If this is not a good solution for you, why don't you try keeping a small VHD locally with just the operating system installed on it, and then add the bulk of the storage onto the NAS? That way, the VM would boot/run as quickly as it should (locally), and the majority of your data would reside on the NAS (and be accessible from all VMs and the host OS).

Edit: unless you are connecting your NAS via SATA, in which case I am unsure of a solution to your issue. As soon as I saw "NAS" I thought of you streaming your VM images over a network...

  • To be clear, I'm not running all three VMs at the same time, I'm just storing them all on the NAS. But yes, I'm connecting over the network, not SATA. Unfortunately I just don't have enough space to move them to the internal drive.
    – daGUY
    Aug 14, 2014 at 22:22
  • @daGUY what about keeping the boot disk VHD locally and storing data VHD(s) on your NAS? You can get away with about 25GB for a Windows 7 boot disk VHD, then attach the other VHDs over the network.
    – aglasser
    Aug 15, 2014 at 15:23

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