Troubleshooting backups to "Same host as VM"

Procedure to check if a Virtual Machine can be manually cloned when backups to "Same host as VM" are failing

Solution

In order to identify the cause of the issue a manual clone can be created by doing this:
1.Snapshot the Virtual Machine
2.Connect to the ESXi server using an SSH client
3.Create the folder "TrileadTest" in [datastore target] by running this command: mkdir /vmfs/volumes/targetdatastore/TrileadTest (please skip this step if the folder still exist in the datastore)
4.Run the clone command: vmkfstools -i "/path/to/disk.vmdk" -d thin "/path/to/cloned.vmdk"

If cloning with vmkfstools works then ESXi logs should be checked for possible input/output errors like:

2015-11-24T08:27:11.710Z [6E481B70 info 'Vimsvc.ha-eventmgr'] Event 826 : Frequent PowerOn Reset Unit Attentions are occurring on device naa.5000c5008bcf76fd. This might indicate a storage problem. Affected datastores: Backup

The root cause for the above error is explained on this VMware KB:

http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1020702.