I ran into a serious problem today. One of our VMWare datastores ran out of disk space so I resized the Volume, then the LUN. I didn't pay attention to the maximum size Limit of 2TB for a VMFS datastore and received an error like:
Call "HostDatastoreSystem.QueryAvailableDisksForVmfs" for object "datastoreSystem-43668" on vCenter Server "" failed.
First I didn't even realize that this is related to the limitation of the datastore. And I started googling for the error and found nothing. What a suprise.
I resized the 1.86 TB LUN to 2.1 TB. All VM's are still running fine but now I wonder if I can decrease the size of the lun to 1.86TB without loosing or damaging the VMFS datastore?
I agree with those that suggest a new LUN. If you shrink a lun you may not necessarily decrease its size by removing free blocks. You dont know where in the lun the free space is, so shrinking it to a smaller size may create more problems than it solves. I have had this same problem a few times and I always took the most cautious path by creating a new volume/lun and emptying the contents of the old before removing it entirely.