Here is a bit of an explanation I pulled from the VMware forums:
As it got mentioned earlier, the coredump partition of older ESX(i) hosts is only 110 MB large, and we have seen coredumps that are larger than that size when collected through netdump, or we have seen incomplete coredumps in case of deployments where only the 110 MB coredump partition was available. With the introduction of ESXi 5.1 we enabled an option to use larger coredump partitions through the boot option "diskDumpSlotSize", however the default partition size still remained at 110 MB, which means a customer needs to reconfigure the host manually. See KB 2012362 [1] for details.To avoid the manual reconfiguration step, we introduced with ESXi 5.5 the coredump file feature. It allows ESXi to determine whether the current host might try to generate a coredump that won't fit into the coredump partition. If such a condition has been identified, ESXi will automatically create the file /vmfs/volumes/<some datastore>/vmkdump/<HW-UUID>.dumpfile with the appropriate size.This means just the presence of the *.dumpfile is no indication of a problem with ESXi, it just indicates that the host is prepared for the case of crash of ESXi and should enable VMware support to retrieve a complete coredump. In case of a crash of ESXi, ESXi will extract the coredump out of the configured dump file and create a vmkernel-zdump* file in /var/core during the first reboot following the crash.For new ESXi 5.5 deployments the coredump partition got increased to 2.5 GB, so that for most fresh deployments a coredump file wouldn't be required.
In order to delete those files one needs to connect to each of the ESXi hosts through the console and run the following command:
esxcli system coredump file list
The command will produce a result similar to this:
Here you can see that there are two dump files. The on listed as active (true) is the one that was generated by the host with an active console connection. In order to remove that file one needs to execute the following command:
esxcli system coredump file remove -F
The files will get recreated next time the ESXi server is rebooted. In order to disable auto-generation of those files one would need to set "autoCreateDumpFile" boot option to FALSE.
