Today after update(just apply the latest bug fix and security patches) our ESXi 5.5 farm had a strange issue.
Applying VMware update in 8 ESXi 5.5 HP DL360 Gen9, after the reboot I had the same issue in all hosts
Warning: No coredump has been configured. Host core dumps cannot be saved
First I try investigate the updates and check any VMware KB information and don't see anything that could cause this issue. Or if is an hidden issue, or the issue was already in this hosts and never been discover.
So we try to find where was the issue here.
Starting to check the partition and look for the partition coredump state.
List all coredump partitions: # esxcli system coredump partition list
It seems there is no coredump partition.
Then check heck the devices in the host: # esxcfg-scsidevs -c
I see the the SD Flash card where the ESXi is installed.
So lets check all partitions in this device and see if there is any partition for the coredump(call vmkDiagnostic) using partedUtil.
List all partitions: # partedUtil getptbl /vmfs/devices/disks/mpx.vmhba32:C0:T0:L0
There is the #7(normally the vmkDiagnostic and coredump partition) but also #9.
So we need to set the coredump into the proper partition and enable and delete the other.
This type of issues(2 coredump partitions) normaly happen in ESXi hosts that were upgraded(these hosts were upgraded from 5.0 to 5.5 some time ago)
First bind the coredump to the right partition: # esxcli system coredump partition set --partition='mpx.vmhba32:C0:T0:L0:7'
Then set the to coredump to true: # esxcli system coredump partition set --enable true
Then just list the coredump partitions again to check if now is set: # esxcli system coredump partition list
As we can see, now the partition #7 is enable and active for coredump, but we still have a second one. So lets just delete the #9 partition.
To delete the partition we need to use the partedUtil again: # partedUtil delete /vmfs/devices/disks/mpx.vmhba32:C0:T0:L0 9
After we delete the partition, lets check if is already remove from the partition table and check if there is only one active coredump partition.
# partedUtil getptbl /vmfs/devices/disks/mpx.vmhba32:C0:T0:L0
All partitions are correct and now only one coredump partitions is visible.
After this coredump is again active and enable and we don't see any warning anymore in the host(in vSphere Client)
Hope this help you correcting your coredump issues.