Can You Run a VM from an External Drive?

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At a recent conference for Mac® IT admins, I was asked, “Can you run a VM from an external drive?”

Short answer: “Yes, absolutely. I do this all the time.”

Longer answer: You have always been able to run a Parallels Desktop® for Mac virtual machine from an external drive. In Parallels Desktop 13, this performance has been significantly improved, if your external drive is an SSD drive connected to your Mac by Thunderbolt.

So that you can see what it’s like to run a VM from an external drive, I made a short video. (See video 1). I have deliberately not changed the video playback speed, or deleted any portion of it, in order for you to get an accurate “feel” of the VM’s performance.

Video 1: Running a Windows 10 VM from an external drive

While this is subjective, I think you’ll agree that this VM’s performance looks the same as a VM on the Mac internal storage. For the definitive word on virtual machine performance on a Mac, see this comprehensive MacTech report.

As you can see in the video (at 00:22), Parallels Desktop does alert you when you boot up a VM stored on an external drive. This is so you do not inadvertently disconnect the external drive while the VM is running. (See figure 1.)

Windows 10 Mac external drive

Figure 1

Here are the details about the setup for this video:

Parallels Desktop 13.2.0

Touch Bar™ MacBook Pro® with 16 GB RAM running High Sierra 10.13.1 (with all patches)

External Drive: SSD2go PKT (1 TB, with USB-C connection)

Windows 10 Fall Creators Update (version 1709) with all patches

Microsoft Office 2016 Version 1710 (Build 8625.2127) with all patches

Microsoft Edge 41.16299.15.0

The easiest way to build a VM that can be used on an external drive is to create that VM in your shared VM folder. Then just move the VM’s pvm file to the external drive, as detailed in this Knowledge Base (KB) article, How to run a virtual machine from network or external mass storage. (If you want to move a VM from your personal VM folder to an external drive, you may need to adjust the VM’s permissions as detailed in the KB article, How to share virtual machine with several user accounts on a Mac.)

I hope this helps you manage the limited storage on your Mac, since you can move an infrequently used VM to an external drive and still use it without a noticeable performance penalty.

Let us know in the comments if you store some VMs on an external drive and what your experiences have been.

If you want to try running a VM from an external drive with Parallels Desktop 13, feel free to get started with our free, full-featured 14-day trial.

Kurt has been a Mac developer since before the Mac came out. Today he is the Senior Product Manager at Parallels where he works on both Parallels Desktop for Mac and Parallels Access. Prior to Parallels, he was the Senior Mac Evangelist in the Macintosh Business Unit (MacBU) at Microsoft Corp. Kurt is the author of three books and has lectured internationally on object-oriented programming, UI design, and virtualization. Kurt is also a Microsoft Office for Mac and iOS Accredited Support Professional for 2014 and 2015. Outside of work, Kurt has been a fencer for many years, has four times been a member of the US team at the world championships, and has also been the coach of the US team: http://www.naginata.org.

2 Comments

  1. Hi Kurt, is it sufficient to have a USB 3.1 Gen2 external SSD, such as Samsung T5 (via USB-C)? This are less than 50% of the cost of a “proper” Samsung Thunderbolt 3 external SSD (such as X5).
    The numbers given are 540 MB/s read/write speed for USB3.1 vs. 2.800 MB/s / 2.300 MB/s read/write speed for Thunderbolt, but I believe it comes down to latency rather than to the (nominal) throughput. So could you please post the results of a (synthetical) benchmark of your SSD? I would than compare it to the benchmarks of T5 and X5. By the way, I have a MacBook Pro 2017, 13 inch, TouchBar. Thanks, Michael

    • Hi Michael,

      I am happy to run a disk benchmark to help you.

      I have several external drives, but my favorite is the 1TB SSD2go from AngelFire.

      The Mac I used:
      MacBook Pro (15-inch, 2016) Touch Bar
      2.9GHz i7
      16 G RAM
      High Sierra 10.13.6

      The benchmark utility I used is the Blackmagic Disk Speed Test downloaded from the Mac App Store.

      The benchmark results for the SSD2go:
      Write: 413.6 MB/s
      Read: 524.5 MB/s

      The benchmark results from the internal SSD:
      Write: 909.5 MB/s
      Read: 2313.4 MB/s

      I was quite surprised by the large differences in the benchmarks for the SSD2Go and the internal SSD.

      I hope this data helps you.

      Kurt

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