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AHCI (vmw_ahci) performance issue resolved in ESXi 6.5 Update 1

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For customers who had SATA controllers that consumed the VMware Advanced Host Controller Interface (AHCI) driver found that after upgrading to ESXi 6.5, the disk performance for those devices were significantly impacted. Basic operations such as cloning or uploading an OVF/OVA would literally double if not triple in time. In fact, I too had observed this same behavior when I had upgraded my Intel NUC (not an officially supported platform) to ESXi 6.5. One thing I had noticed at the time when others were reporting simliar issues was that their HW platforms were also not on the VMware HCL, so I was not sure if this was limited to only home-lab environments?

In any case, I and others eventually stumbled onto this blog article by Sebastian Foss who I believe may have been the first to identify a workaround which was to simply disable the new AHCI Native Driver which loads by default and forcing it fall back to using the legacy AHCI driver which made the issue go away after a reboot. Although the folks who had reported seeing simliar issue were all using hardware platforms that were not officially on the VMware HCL, I decided to still file an internal bug and hoped someone could take a look to see what was going on.

With the release of ESXi 6.5 Update 1, I am happy to report the observed performance issues with the Native AHCI driver have now been resolved! I have been running on earlier release of ESXi 6.5 Update 1 build for couple of weeks now and have not seen any of the problems I had before. For those interested, the official fix went is in version 1.0.0-37vmw or greater of the vmw_ahci driver.

You can easily verify for this by running the following ESXCLI command to retrieve the version of your vmw_ahci driver:


If you had disabled the Native AHCI driver, you will definitely want to re-enable it. You can check if its been disabled by running the following ESXCLI command and checking the second column to see if it shows "false":

esxcli system module list | grep vmw_ahci

If the Native AHCI driver is disabled as shown in the previous command, then you can re-enable it by running the following ESXCLI command:

esxcli system module set --enabled=true --module=vmw_ahci

Once you have re-enabled the driver, you will need to reboot for the changes to go into effect.

ESXi 6.5 support for Apple Mac Pro 6,1

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I know several of you have reached out asking about the support for ESXi 6.5 on the Apple Mac Pro 6,1 but as of right now, the Mac Pro 6,1 is currently not supported with ESXi 6.5. I know this is not ideal especially for customers who wish to take advantage of the latest vSphere release. The good news is that VMware is in the process of testing the Apple Mac Pro 6,1 for ESXi 6.5, however there is not an ETA on when this will be completed by.

Some of you might be wondering why this did not happen earlier? The primary reason is that hardware certification for ESXi is actually performed by the hardware vendors. Once a vendor completes the certification for a particular hardware platform or component, they submit the results to VMware and the VMware HCL is updated. If there is a piece of hardware that is not on the VMware HCL today, it is definitely worth reaching out to your hardware vendor to inquire about its status.

In Apple's case, it unfortunate as they do not participate in VMware's Hardware Certification program for ESXi which makes certification challenging. VMware intends to continue to support customers who require the use of Mac OS X Virtualization and will work towards getting the Mac Pro's certified for latest version of vSphere as mentioned earlier. Historically, testing and certifying ESXi for Apple hardware does take an additional amount of time and in some cases, code changes may even be required due to unexpected hardware changes from Apple.

I hope this gives customers some additional insights into how Apple hardware is certified for ESXi. If you would like to see this improved in the future, you may want to reach out to Apple and provide them with your feedback.

Now ... before you close this blog post thinking it is going to take awhile before there is going to be an update regarding ESXi 6.5 and Mac Pro 6,1, please continue reading further 🙂

UPDATE (07/28/2017) - ESXi 6.5 Update 1 just GA'ed yesterday and is fully supported with all current Apple Mac Pro 6,1 (as you can see on the HCL here) and the workaround mentioned below is no longer required. This means you can install ESXi without any modification to the image.

UPDATE (03/25/2017) - VMware has just published the following VMware KB 2149537 which outlines the officially recommended workaround to install ESXi 6.5 onto the Apple Mac Pro 6,1. The VMware HCL has also been updated to include the Apple Mac Pro 6,1 4-Core, 6-Core, 8-Core & 12-Core systems. In a future release of ESXi, the workaround will not be required and ESXi will just install out of the box. This temporarily workaround is to enable customers who wish to run the current version of ESXi 6.5 which includes GA release, 6.5a and 6.5p01.

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