ESXi Disk Full.
While working in my Lab, I was rebuilding an ESXi host and began to run into a strange issue. I was unable to save any configuration changes to the host from within vCenter. The server was a brand new installation yet was complaining about having no access to write to the disk.
After restarting the host, I would be able to make configuration changes for 3 – 5 minutes from when the machine started before beginning to experience updating errors. The error seemed to indicate that the hard disk was full and it was unable to write configuration changes to /etc/vmware/esx.conf.
My particular lab runs a non standard *(non supported) motherboard (SuperMicro X8SIL) that seems to have some issues with the VMware implementation of CIM. The Common Information Model is used to gather information about actual sensors in the hardware. Since my board did not play nice with VMware, it flooded the log files and thus after a couple of minutes from boot up, the disk would fill. A quick fix was to disable the Sensor Dashboard in advanced settings.
After restarting the host and BEFORE the disk filled, quickly change the Advanced Host value UserVars.CIMEnabled from 1 to 0. This corrected the issue immediately. Of course, I sacrificed the ability to view the board sensors from within Virtual Center.