Slow data copy to external USB drive plugged into ESX host and passed to Windows VM


We have a USB drive plugged into an ESX 6.0 host and passed to a Windows VM. The problem we have is the very slow transfer to the drive and/or the transfer freezes for minutes at a time. When looking at Resource Monitor during the transfer, the disk activity and queue length are at 100% and the USB drive becomes unresponsive. When the transfer completes the disk activity drops back to 0% (ish).
A 1GB file gets to 99.9% in a few seconds, then takes 4-5 mins to do the last 40mb. Or sometimes it will do 50% and freeze for a few minutes and then do the other 50% in seconds. Very random.
Copying to the OS drive has no problems so it definitely relates to USB. We have tried 2 different USB drives, 2 different Windows VMs and two different ESX servers from different manufacturers. All of them have this same problem.

I have found an article on VMware forums but there is no answer, however it shows that the problem also occurs on other versions:

Thanks in advance.
Marc JacobsAsked:
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
This is to be expected, USB transfer I/O is virtualised, USB was designed for the addition of USB security keys and tokens, e.g. "dongles" not the addition of USB backup devices.

So therefore it's slow, I would recommend Network Transfer to a NAS, or if you want to carry on using USB, add the USB PCI card to the VM, using VM Direct Path

see this article

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Marc JacobsAuthor Commented:
Thanks Andrew.

The VM Direct Path works perfectly.
Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
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