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Quick Tip - Enabling ESXi Coredumps to be stored on USB

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I was recently working with Engineering to reproduce an issue which causes an ESXi PSOD (Purple Screen of Death) and I wanted the generated ESXi coredump to simply write to the USB device, which I could easily grab.

As of ESXi 7.x, I know we had removed a few of the old ESXi kernel boot options for allowing ESXi to store coredumps on a USB device and the using the ESXi kernel boot option allowCoreDumpOnUsb=TRUE should now be used, however I was struggling to get it to work.

Since I was using a debug version of ESXi, I needed to install ESXi from scratch and I thought I could simpply add the required kernel option, as shown in the screenshot below, and I had assumed it would automatically configure the ESXi coredump file to be stored on the VMFS-L volume residing on the USB device.


After a couple of attempts, I finally realized that this particular ESXi kernel boot option, is literally that, a boot option that is only applicable after the initial ESXi installation. 🤦 Unlike other ESXi kernel boot options which can be used during the initial installation which would apply certain configuration changes, this setting applies after ESXi has been installed. Once I appended the setting, the ESXi coredump file was created in the VMFS-L volume and I was then able to reproduce the issue and generate vm-support bundle that included the coredump!

How to disable the Efficiency Cores (E-cores) on an Intel NUC?

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The Intel 12th Generation (Alder Lake) CPU is the first Intel consumer CPU that introduces a new hybrid big.LITTLE CPU architecture. This new hybrid Intel CPU architecture integrates two types of CPU cores: Performance-cores (P-cores) and Efficiency-cores (E-cores) into the same physical CPU die. For more information about this new hybrid Intel CPU design, check out this resource HERE.

These new hybrid Intel CPUs have also become the defacto standard for the Intel NUCs starting with the 12th Generation Intel NUCs (Dragon Canyon, Wall Street Canyon & Serprent Canyon), which were released last year. While the ESXi scheduler does not support or understand this new consumer CPU architecture, it can function with ESXi but does require an ESXi kernel boot option, which I have documented HERE, that tells ESXi to ignore the CPU differences.

While this has been an acceptable workaround, there are no guarantees on how the ESXi scheduler will behave. Furthermore, you will also not benefit from Hyper-threading (HT) on the P-cores as the E-cores do not contain HT-enabled cores and hence HT is also disabled by ESXi. A slightly better workaround is to actually disable the E-cores, which would give you uniform CPU P-cores and also access to HT. During my initial investigation, I was never able to figure out how to disable the E-cores within the Intel NUC BIOs and I had assumed it was just not possible.

I recently had re-inquired about this configuration change and came to learn that it is possible to change both the P-core and E-core settings within the Intel NUC BIOs, it was just not very intuitive!

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Changing the default HTTP(s) Reverse Proxy Ports on ESXi 8.0

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The process of changing the default ports for the ESXi Reverse Proxy service has always been pretty straight forward, which I had also shared back in 2015 HERE. While most customers stick with the default configuration (80 for HTTP and 443 for HTTPS), we do have some customers that need to change these ports to meet certain organization security and/or compliance requirements.

Disclaimer: VMware does not officially support modifying the default HTTP/HTTPS ports on an ESXi host.

I recently came across a customer report where the previous method for changing the ESXi Reverse Proxy ports on an 8.0 host no longer worked and the only thing that was shared was that the user could no longer run ESXCLI directly within the ESXi Shell, which I thought was a strange observation.

I deployed the latest ESXi 8.0b as a Nested ESXi VM and I went through the instructions I had outlined in my blog post HERE and changed the HTTPS port from 443 to 4444, which was the setup the user was looking to do and I ran into the exact same issue. At first, I thought maybe we actually no longer support this capability and decided to quickly test by using the remote version of ESXCLI, which allows you to specify a port as part of the connection and it failed with the same error.

UPDATE (07/31/23) - For ESXi 8.0 Update 1 instructions, please refer to this blog post HERE.

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