I was making some changes to the vmfocus.com lab the other day and kept getting a repeated error Call “HostStorageSystem.UnmountVmfsVolume” for object “storageSystem-15” on vCenter Server when I was trying to unmount a VMFS Datastore
When I went to unmount the VMFS Datastore it met all the relevant criteria.
Resolution
If you are booting from flash device such as a USB or internal SD card, then a VMFS Datastore would have been selected to store your output logs for troubleshooting.
These need to be moved to a VMFS Datastore which you are going to keep.
Note: You will need to make these changes to each ESXi Host
Select ESXi Host > Configuration > Advanced Settings > Syslog > Syslog.global.logDir
Change the paramters to a VMFS Datastore that will remain e.g.
[ESXi01_RAID10_L01_SAS] /scratch/log
Hit OK and then you will have success in unmounting your VMFS Datastore.
VMFocus 