Plan for vSphere core dump on diskless hosts

BootInstalling VMware vSphere on hardware come with many options when it comes to the location of the many partitions necessary for ESXi. ESXi can be installed on USB, SD (mini) cards, local storage, and boot from LUNs. Before you deploy your ESXi hosts, you should be thinking about your design and the limitations (is any) of each of the boot options.

Remember that ESXi has several partitions that are created during its installation.

7 Partitions:

  1. System Partition
  2. Linux Native – /scratch
  3. VMFS datastore
  4. n/a
  5. Linux Native /bootbank
  6. Linux Native /altbootbank
  7. vmkDiagnostics
  8. Linux Native /store

One thing to note is that partition 2 & 3 (/scratch & VMFS) are not present on the image below. This is because my ESXi host was installed on an SD card.

ESXi_Partitions

 

This post will focus on the vmkDiagnostics partition. VMware recommends that this partition is kept on local storage unless it is a diskless installation, such as boot from SAN. I have seen a rapid increase on boot from SAN as more and more people are transitioning into Cisco’s UCS blades. So, if you are doing this or planning on booting from SAN, make sure that you create a core dump partition for your hosts. You have a few options to do this.

  • You could have the core dumps on the boot LUN; however, it is recommended that a separate LUN is created for this partition.
    • Independent HW iSCSI only (keep reading).
  • If you set the diagnostic partition to be at the boot LUN, make sure only that host has access to it.
    • This should already be the case anyway. A boot LUN should only be accessible to the specific host.
  • IF you create a separate LUN for the diagnostic partition, you can share this LUN among many hosts.
  • You can also set up a file as a core dump location on a VMFS datastore (see caveat below).

 

That sounds pretty easy right?!? Yes but wait, there is a big caveat here. 

You CANNOT place the diagnostic partition on any of the options above if using software iSCSI or hardware dependent initiators (iBFT). This can only be done via independent hardware iSCSI. More info here. This is not version dependent at the time this post was written.

 

Now what?

If do not have any hardware HBAs, you have a couple of options.

  1. The recommended option is to set up ESXi Dump Collector
    • Requires configuration on vCenter (Windows and VCSA)
    • Available for vSphere 5.0 and later
    • Consolidates logs from many hosts
    • Easily deployed via Host Profiles or esxcli commands
  2. You could also put this on USB storage, but this requires disabling the USB Arbitrator service, which means that you will not be able to use USB passthrough on any VM.
    • I personally wouldn’t recommend this option.

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