I had a customer with six blades booting from iSCSI.

ESXi sees this as a software iSCSI initiator and will not let you put a diag partition on the storage.

You will see an error message like this in the host summary.  No vmcore disk partition is available and no network coredump server has been configured. Host core dumps cannot be saved.

So to fix the above error you need to install the Dump Collector on the vCenter. It isn’t what you think, there are no toilets involved.

Next you need to enable ssh on each host and enter these commands

esxcli system coredump network set -v vmk0 -i 192.168.100.209 -o 6500

esxcli system coredump network set --enable true

esxcli system coredump network get

In my case 192.168.100.209 was the vCenter server running on port 6500. The last command just verifies those were set.

I am also assuming that vmk0 is your management nic. You can verify that by the ol’ esxcfg-vmknic –l command

Once you run those commands you should get an output like this:

Exit out, turn off SSH and your errors will be gone, no reboots needed.