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steve_bakes
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I/O Performance slow on USB SSD

I'm using Workstation 14.0 on Linux (Ubuntu 17.04). I purchased a Samsung T5 USB-C SSD, which performs very well when copying files to/from the device. However, once I start a VM stored on the SSD, I/O performance dives. Reading a file off the disk slows from ~ 300MB/s to 5-12 MB/s (using 'dd' from command line, file not used by the VM). Write performance suffers similarly when VM is running, fine when I power off guest VM. Shutting off the VM whilst read/write operation in progress instantly restores the higher speed. What is happening?

Note that this problem does NOT occur when using mechanical USB HDD on same computer. Can start VM on the HDD, wait until it boots and it idle, then can read/write files at normal full speed of the HDD.

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steve_bakes
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I found the answer. The external SSD was formatted with exFAT, which VMWare seemingly does not like. Not only does the VM performance suffer tremendously, but all other I/O external to VMWare ALSO suffers when a VM stored on the SSD is running.

Re-formatting the SSD with NTFS restored the performance back to normal levels. I don't understand why Workstation should not support exFAT at full speed, either it's a bug/feature of Workstation or possibly it's a limitation of exFAT.

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AishR
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Please refer to KB VMware Knowledge Base  that may shed more light on this issue.

It would be interesting to see the top command also in the Linux Guest when doing the dd command. Also ensure that VMware tools is installed and running fine inside the Guest OS.

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steve_bakes
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Thanks for the reply AishR. I looked over the KB article but it refers to poor performance in the guest VMs. In my case the guest VMs perform normally, but when the host OS copies a large file to the same USB SSD on which the running VMs are stored the copy performs very slowly. Sorry, this should have been more clear in my original post.

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wila
Immortal
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Hi,

From reading other reports I get the feeling that this is a Workstation 14.0 issue.

This was no problem in Workstation 12.5 AFAIK.

--

Wil

| Author of Vimalin. The virtual machine Backup app for VMware Fusion, VMware Workstation and Player |
| More info at vimalin.com | Twitter @wilva
steve_bakes
Contributor
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I found the answer. The external SSD was formatted with exFAT, which VMWare seemingly does not like. Not only does the VM performance suffer tremendously, but all other I/O external to VMWare ALSO suffers when a VM stored on the SSD is running.

Re-formatting the SSD with NTFS restored the performance back to normal levels. I don't understand why Workstation should not support exFAT at full speed, either it's a bug/feature of Workstation or possibly it's a limitation of exFAT.