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Quick Tip - Suppress new core dump warning in ESXi 7.0

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You may have noticed new warning message after installing ESXi 7.0, this can happen if your ESXi installation is on a smaller local disk (Nested ESXi Appliance would also be affected) which does not have enough capacity for setting up a core dump target or if ESXi is booting from USB which also does not support core dumps by default.

No coredump target has been configured. Host core dumps cannot be saved.


It is certainly recommended that you have a core dump target configured, especially for Production systems. However, if you wish to suppress the warning, there is an ESXi Advance Setting which you can toggle called UserVars.SuppressCoredumpWarning (can be configure using Embedded ESXi Host Client or vSphere UI in vCenter Server) as well as ESXCLI. Below is the command to suppress the warning:

esxcli system settings advanced set -o /UserVars/SuppressCoredumpWarning -i 1

Changing the default size of the ESX-OSData volume in ESXi 7.0

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In ESXi 7.0, a new partition scheme was introduced which also brings along a new set of storage requirements. These changes are explained in the official documentation here and the following VMware KB 77009 also contains some additional info which can be helpful. Storage changes are not easy but this was necessary to not only better support some of the current capabilities but more importantly, it setups the foundation for future ESXi capabilities.

The biggest change to the partition layout is the consolidation of VMware Tools Locker, Core Dump and Scratch partitions into a new ESX-OSData volume (based on VMFS-L). This new volume can vary in size (up to 138GB) depending on a number of factors including the current ESXi boot media (USB SD-Card, Local Disk) but also the size of the device itself, which is explained in the official documentation.

From some of the comments on Twitter, Reddit and the direct inquiries that I have received, this new behavior seems to be most impactful to smaller homelabs where a fresh install of ESXi 7.0 has been performed. Folks have shared that their ESX-OSData volume has taken up 120GB which can be quite significant if you have a smaller disk which can be quite common. I normally install ESXi on a USB device and I also use vSAN, which has a different behavior and I have also not upgraded my physical ESXi host (E200-8D) to 7.0 yet.

I performed a fresh installation of ESXi 7.0 (running as Nested ESXi VM) that was configured with 1TB of storage and here is what the filesystem layout now looks:


We can see that the ESX-OSData volume takes up ~119.75GB, which is not too bad for 1TB volume but I can understand this may not be ideal if you have something smaller such as 250GB to 512GB disk. Due to the size of the local device, the boot options mentioned in the KB would not be helpful and I was curious myself if this ESX-OSData volume size could be configurable. In doing some research it looks like the size of the ESX-OSData can be specified using the following ESXi boot option (SHIFT+O during the initial boot) called autoPartitionOSDataSize

UPDATE (12/17/20) - Official support for specifying the size of ESX-OSData has been added to the release of ESXi 7.0 Update 1c with a new ESXi kernel boot option called systemMediaSize which takes one of four values:

  • min = 25GB
  • small = 55GB
  • default = 138GB (default behavior)
  • max = Consumes all available space

If you do not require or have 138GB for the ESX-OSData, you can override the default behavior by appending this option with the specified value (e.g. systemMediaSize=min). It is worth noting that by using this setting, the smallest ESX-OSData volume you can configure is 25GB. For homelabs or environment which require less than this, you would have to use the unsupported autoPartitionOSDataSize parameter , which is not officially supported as mentioned below.

Disclaimer: This may not be officially supported by VMware as it deviates from the system defaults and can have other unintended behaviors. Use at your own risk.

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Heads Up - Nested ESXi crashes in ESXi 7.0 running on older CPUs

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Thanks to Patrik Kernstock, who works in our Technical Support organization at VMware, for making me aware of an issue related to Nested ESXi running on an ESXi host that has been upgraded to ESXi 7.0. Several folks in the community have noticed after upgrading their Intel NUC 7th Gen and deploying a Nested ESXi VM and powering on an inner-guestOS would causes the Nested ESXi VM to crash.

Upon further investigation, it looks like this is not specific to the Intel NUC platform but rather with a specific generation of CPUs which are Intel Sky Lake-based and as a result, some customers are noticing this affect on their 7th Gen NUC.

UPDATE (06/23/20) - ESXi 7.0b has just been released and contains the fix for the Nested ESXi VM crash. If you are using an Intel NUC 10, do not just apply the patch as the updated ne1000 VIB within the patch will override existing Intel NIC driver causing the network adapter to no longer function. It is recommended that you download the patch and replace the default ne1000 VIB using Image Builder with the Intel NIC version before applying the update. To download the patch, please visit VMware Patch Portal site.

The good news is that this issue has already been reported and we should have a fix in a future update of ESXi. In the meantime, you can still run Nested ESXi and Nested Virtualization on these affected CPUs, you just will not be able to power on inner-guest VMs. Big thanks to Patrik for helping out with the testing and triaging this internally.