Description of problem:

VM fails to start with an error of "Failed to acquire lock: No space left on device".

~~~

2019-04-08 11:05:46,811+0200 ERROR (vm/994025f9) [virt.vm] (vmId='994025f9-58a2-49c7-b98c-f1b0e5ac95d7') The vm start process faile
d (vm:949)
Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/vdsm/virt/vm.py", line 878, in _startUnderlyingVm
    self._run()
  File "/usr/lib/python2.7/site-packages/vdsm/virt/vm.py", line 2894, in _run
    dom.createWithFlags(flags)
  File "/usr/lib/python2.7/site-packages/vdsm/common/libvirtconnection.py", line 130, in wrapper
    ret = f(*args, **kwargs)
  File "/usr/lib/python2.7/site-packages/vdsm/common/function.py", line 92, in wrapper
    return func(inst, *args, **kwargs)
  File "/usr/lib64/python2.7/site-packages/libvirt.py", line 1110, in createWithFlags
    if ret == -1: raise libvirtError ('virDomainCreateWithFlags() failed', dom=self)
libvirtError: Failed to acquire lock: No space left on device
2019-04-08 11:05:46,812+0200 INFO  (vm/994025f9) [virt.vm] (vmId='994025f9-58a2-49c7-b98c-f1b0e5ac95d7') Changed state to Down: Fai
led to acquire lock: No space left on device (code=1) (vm:1689)

~~~

Version-Release number of selected component (if applicable):
vdsm-4.20.47-1.el7ev.x86_64
libvirt-4.5.0-10.el7_6.6.x86_64
libvirt-client-4.5.0-10.el7_6.6.x86_64
sanlock-3.6.0-1.el7.x86_64
qemu-kvm-rhev-2.12.0-18.el7_6.3.x86_64

How reproducible:
Very rarely seen.
Seen on the customer's system only once.

Steps to Reproduce:
1.
2.
3.

Actual results:
The VM does not start with the above mentioned error.

Expected results:
The VM should start without problems.

Additional info:

The problem was seen with a Normal VM with a lease.

This was seen on a customer system where they tried to start the VM and it failed with the error "Failed to acquire lock: No space left on device."

The problem seemed to auto correct itself, after the customer collected the log-collector and sosreport of the Hosts, they could start the VM.

The problem here is that the error messages "No space left on Device" is incorrect, there was space on the storage domain.

The primary concern of the customer was that the error message "No space left on device" was misleading and seeks a justification on that.