We had a drive in our NAS fail, but afterwards one of our VM's will not start.

The boot drive on the VM is (so near as I can tell) the only drive affected.

I confirmed that the disk images (active and snapshot) are both valid with qemu.

I followed the instructions at https://www.canarytek.com/2017/07/02/Recover_oVirt_Illegal_Snapshots.html to identify the snapshot images that were marked "invalid" and marked them as valid.

    update images set imagestatus=1 where imagestatus=4;

2020-01-09 02:18:44,908-0600 INFO  (vm/c5d0a42f) [vdsm.api] START prepareImage(sdUUID='6e627364-5e0c-4250-ac95-7cd914d0175f', spUUID='25cd9bfc-bab6-11e8-90f3-78acc0b47b4d', imgUUID='4081ce8f-1ce1-4ee1-aa43-69af2dfc5ab6', leafUUID='f8066c56-6db1-4605-8d7c-0739335d30b8', allowIllegal=False) from=internal, task_id=26053225-6569-4b73-abdd-7d6c7e15d1e9 (api:46)
2020-01-09 02:18:44,931-0600 INFO  (vm/c5d0a42f) [vdsm.api] FINISH prepareImage error=Cannot prepare illegal volume: (u'f8066c56-6db1-4605-8d7c-0739335d30b8',) from=internal, task_id=26053225-6569-4b73-abdd-7d6c7e15d1e9 (api:50)
2020-01-09 02:18:44,932-0600 ERROR (vm/c5d0a42f) [storage.TaskManager.Task] (Task='26053225-6569-4b73-abdd-7d6c7e15d1e9') Unexpected error (task:875)
Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/vdsm/storage/task.py", line 882, in _run
    return fn(*args, **kargs)
  File "<string>", line 2, in prepareImage
  File "/usr/lib/python2.7/site-packages/vdsm/common/api.py", line 48, in method
    ret = func(*args, **kwargs)
  File "/usr/lib/python2.7/site-packages/vdsm/storage/hsm.py", line 3187, in prepareImage
    raise se.prepareIllegalVolumeError(volUUID)
prepareIllegalVolumeError: Cannot prepare illegal volume: (u'f8066c56-6db1-4605-8d7c-0739335d30b8',)
2020-01-09 02:18:44,932-0600 INFO  (vm/c5d0a42f) [storage.TaskManager.Task] (Task='26053225-6569-4b73-abdd-7d6c7e15d1e9') aborting: Task is aborted: "Cannot prepare illegal volume: (u'f8066c56-6db1-4605-8d7c-0739335d30b8',)" - code 227 (task:1181)
2020-01-09 02:18:44,933-0600 ERROR (vm/c5d0a42f) [storage.Dispatcher] FINISH prepareImage error=Cannot prepare illegal volume: (u'f8066c56-6db1-4605-8d7c-0739335d30b8',) (dispatcher:82)
2020-01-09 02:18:44,933-0600 ERROR (vm/c5d0a42f) [virt.vm] (vmId='c5d0a42f-3b1e-43ee-a567-7844654011f5') The vm start process failed (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 2798, in _run
    self._devices = self._make_devices()
  File "/usr/lib/python2.7/site-packages/vdsm/virt/vm.py", line 2639, in _make_devices
    disk_objs = self._perform_host_local_adjustment()
  File "/usr/lib/python2.7/site-packages/vdsm/virt/vm.py", line 2712, in _perform_host_local_adjustment
    self._preparePathsForDrives(disk_params)
  File "/usr/lib/python2.7/site-packages/vdsm/virt/vm.py", line 1023, in _preparePathsForDrives
    drive['path'] = self.cif.prepareVolumePath(drive, self.id)
  File "/usr/lib/python2.7/site-packages/vdsm/clientIF.py", line 417, in prepareVolumePath
    raise vm.VolumeError(drive)
VolumeError: Bad volume specification {'address': {'bus': '0', 'controller': '0', 'type': 'drive', 'target': '0', 'unit': '0'}, 'serial': '4081ce8f-1ce1-4ee1-aa43-69af2dfc5ab6', 'index': 0, 'iface': 'scsi', 'apparentsize': '36440899584', 'specParams': {}, 'cache': 'writeback', 'imageID': '4081ce8f-1ce1-4ee1-aa43-69af2dfc5ab6', 'truesize': '16916186624', 'type': 'disk', 'domainID': '6e627364-5e0c-4250-ac95-7cd914d0175f', 'reqsize': '0', 'format': 'cow', 'poolID': '25cd9bfc-bab6-11e8-90f3-78acc0b47b4d', 'device': 'disk', 'path': '/rhev/data-center/25cd9bfc-bab6-11e8-90f3-78acc0b47b4d/6e627364-5e0c-4250-ac95-7cd914d0175f/images/4081ce8f-1ce1-4ee1-aa43-69af2dfc5ab6/f8066c56-6db1-4605-8d7c-0739335d30b8', 'propagateErrors': 'off', 'name': 'sda', 'bootOrder': '1', 'volumeID': 'f8066c56-6db1-4605-8d7c-0739335d30b8', 'diskType': 'file', 'alias': 'ua-4081ce8f-1ce1-4ee1-aa43-69af2dfc5ab6', 'discard': False}
2020-01-09 02:18:44,934-0600 INFO  (vm/c5d0a42f) [virt.vm] (vmId='c5d0a42f-3b1e-43ee-a567-7844654011f5') Changed state to Down: Bad volume specification {'address': {'bus': '0', 'controller': '0', 'type': 'drive', 'target': '0', 'unit': '0'}, 'serial': '4081ce8f-1ce1-4ee1-aa43-69af2dfc5ab6', 'index': 0, 'iface': 'scsi', 'apparentsize': '36440899584', 'specParams': {}, 'cache': 'writeback', 'imageID': '4081ce8f-1ce1-4ee1-aa43-69af2dfc5ab6', 'truesize': '16916186624', 'type': 'disk', 'domainID': '6e627364-5e0c-4250-ac95-7cd914d0175f', 'reqsize': '0', 'format': 'cow', 'poolID': '25cd9bfc-bab6-11e8-90f3-78acc0b47b4d', 'device': 'disk', 'path': '/rhev/data-center/25cd9bfc-bab6-11e8-90f3-78acc0b47b4d/6e627364-5e0c-4250-ac95-7cd914d0175f/images/4081ce8f-1ce1-4ee1-aa43-69af2dfc5ab6/f8066c56-6db1-4605-8d7c-0739335d30b8', 'propagateErrors': 'off', 'name': 'sda', 'bootOrder': '1', 'volumeID': 'f8066c56-6db1-4605-8d7c-0739335d30b8', 'diskType': 'file', 'alias': 'ua-4081ce8f-1ce1-4ee1-aa43-69af2dfc5ab6', 'discard': False} (code=1) (vm:1689)
2020-01-09 02:18:44,963-0600 INFO  (vm/c5d0a42f) [virt.vm] (vmId='c5d0a42f-3b1e-43ee-a567-7844654011f5') Stopping connection (guestagent:442)
2020-01-09 02:18:44,978-0600 INFO  (jsonrpc/4) [api.virt] START destroy(gracefulAttempts=1) from=::ffff:192.168.2.15,57858, flow_id=4b57f1a6, vmId=c5d0a42f-3b1e-43ee-a567-7844654011f5 (api:46)
2

Log excerpt from attempt to migrate the affected drive to another storage device:

2020-01-09 05:27:14,362-0600 INFO  (jsonrpc/2) [storage.VolumeManifest] ec6ccb14-03c2-49cc-9cc0-b1a87d582ed7/4081ce8f-1ce1-4ee1-aa43-69af2dfc5ab6/f8066c56-6db1-4605-8d7c-0739335d30b8 info is {'status': 'OK', 'domain': 'ec6ccb14-03c2-49cc-9cc0-b1a87d582ed7', 'voltype': 'LEAF', 'description': 'None', 'parent': 'a912e388-d80d-4f56-805b-ea5e2f35d741', 'format': 'COW', 'generation': 0, 'image': '4081ce8f-1ce1-4ee1-aa43-69af2dfc5ab6', 'ctime': '1578559013', 'disktype': 'DATA', 'legality': 'LEGAL', 'mtime': '0', 'apparentsize': '219008', 'children': [], 'pool': '', 'capacity': '1503238553600', 'uuid': u'f8066c56-6db1-4605-8d7c-0739335d30b8', 'truesize': '26624', 'type': 'SPARSE', 'lease': {'path': u'/rhev/data-center/mnt/192.168.2.223:_mnt_ovirt-main-pool/ec6ccb14-03c2-49cc-9cc0-b1a87d582ed7/images/4081ce8f-1ce1-4ee1-aa43-69af2dfc5ab6/f8066c56-6db1-4605-8d7c-0739335d30b8.lease', 'owners': [], 'version': None, 'offset': 0}} (volume:282)
2020-01-09 05:27:14,362-0600 INFO  (jsonrpc/2) [vdsm.api] FINISH getVolumeInfo return={'info': {'status': 'OK', 'domain': 'ec6ccb14-03c2-49cc-9cc0-b1a87d582ed7', 'voltype': 'LEAF', 'description': 'None', 'parent': 'a912e388-d80d-4f56-805b-ea5e2f35d741', 'format': 'COW', 'generation': 0, 'image': '4081ce8f-1ce1-4ee1-aa43-69af2dfc5ab6', 'ctime': '1578559013', 'disktype': 'DATA', 'legality': 'LEGAL', 'mtime': '0', 'apparentsize': '219008', 'children': [], 'pool': '', 'capacity': '1503238553600', 'uuid': u'f8066c56-6db1-4605-8d7c-0739335d30b8', 'truesize': '26624', 'type': 'SPARSE', 'lease': {'path': u'/rhev/data-center/mnt/192.168.2.223:_mnt_ovirt-main-pool/ec6ccb14-03c2-49cc-9cc0-b1a87d582ed7/images/4081ce8f-1ce1-4ee1-aa43-69af2dfc5ab6/f8066c56-6db1-4605-8d7c-0739335d30b8.lease', 'owners': [], 'version': None, 'offset': 0}}} from=::ffff:192.168.2.15,57858, flow_id=94ad3bf0-c5f5-4d45-af2a-49aa4eaa6731, task_id=28e885f7-df18-4ea5-bb6e-eaee7385b519 (api:52)
2020-01-09 05:27:14,363-0600 INFO  (jsonrpc/2) [jsonrpc.JsonRpcServer] RPC call Volume.getInfo succeeded in 0.04 seconds (__init__:573)
2020-01-09 05:27:14,394-0600 INFO  (jsonrpc/6) [vdsm.api] START sdm_copy_data(job_id=u'9a47a14f-d398-4fe8-81fa-59cba7122aa0', source={u'img_id': u'4081ce8f-1ce1-4ee1-aa43-69af2dfc5ab6', u'sd_id': u'6e627364-5e0c-4250-ac95-7cd914d0175f', u'endpoint_type': u'div', u'vol_id': u'f8066c56-6db1-4605-8d7c-0739335d30b8'}, destination={u'generation': 0, u'img_id': u'4081ce8f-1ce1-4ee1-aa43-69af2dfc5ab6', u'sd_id': u'ec6ccb14-03c2-49cc-9cc0-b1a87d582ed7', u'endpoint_type': u'div', u'vol_id': u'f8066c56-6db1-4605-8d7c-0739335d30b8'}) from=::ffff:192.168.2.15,57858, flow_id=94ad3bf0-c5f5-4d45-af2a-49aa4eaa6731, task_id=f1504b2d-c6c2-4866-97ce-e0476b0ba9a2 (api:46)
2020-01-09 05:27:14,395-0600 INFO  (jsonrpc/6) [vdsm.api] FINISH sdm_copy_data return=None from=::ffff:192.168.2.15,57858, flow_id=94ad3bf0-c5f5-4d45-af2a-49aa4eaa6731, task_id=f1504b2d-c6c2-4866-97ce-e0476b0ba9a2 (api:52)
2020-01-09 05:27:14,395-0600 INFO  (jsonrpc/6) [jsonrpc.JsonRpcServer] RPC call SDM.copy_data succeeded in 0.00 seconds (__init__:573)
2020-01-09 05:27:14,396-0600 INFO  (tasks/4) [storage.ThreadPool.WorkerThread] START task f1504b2d-c6c2-4866-97ce-e0476b0ba9a2 (cmd=<bound method Task.commit of <vdsm.storage.task.Task instance at 0x7ff3a42613b0>>, args=None) (threadPool:208)
2020-01-09 05:27:14,396-0600 INFO  (tasks/4) [root] Running job u'9a47a14f-d398-4fe8-81fa-59cba7122aa0'... (jobs:183)
2020-01-09 05:27:14,429-0600 INFO  (jsonrpc/1) [api.host] START getJobs(job_type=u'storage', job_ids=[u'9a47a14f-d398-4fe8-81fa-59cba7122aa0']) from=::ffff:192.168.2.15,57858, flow_id=94ad3bf0-c5f5-4d45-af2a-49aa4eaa6731 (api:46)
2020-01-09 05:27:14,430-0600 INFO  (jsonrpc/1) [api.host] FINISH getJobs return={'status': {'message': 'Done', 'code': 0}, 'jobs': {u'9a47a14f-d398-4fe8-81fa-59cba7122aa0': {'status': 'running', 'job_type': 'storage', 'id': u'9a47a14f-d398-4fe8-81fa-59cba7122aa0', 'description': 'copy_data'}}} from=::ffff:192.168.2.15,57858, flow_id=94ad3bf0-c5f5-4d45-af2a-49aa4eaa6731 (api:52)
2020-01-09 05:27:14,430-0600 INFO  (jsonrpc/1) [jsonrpc.JsonRpcServer] RPC call Host.getJobs succeeded in 0.00 seconds (__init__:573)
2020-01-09 05:27:14,459-0600 INFO  (tasks/4) [storage.SANLock] Acquiring Lease(name='f8066c56-6db1-4605-8d7c-0739335d30b8', path=u'/rhev/data-center/mnt/192.168.2.223:_mnt_ovirt-main-pool/ec6ccb14-03c2-49cc-9cc0-b1a87d582ed7/images/4081ce8f-1ce1-4ee1-aa43-69af2dfc5ab6/f8066c56-6db1-4605-8d7c-0739335d30b8.lease', offset=0) for host id 2 (clusterlock:386)
2020-01-09 05:27:14,496-0600 INFO  (tasks/4) [storage.SANLock] Successfully acquired Lease(name='f8066c56-6db1-4605-8d7c-0739335d30b8', path=u'/rhev/data-center/mnt/192.168.2.223:_mnt_ovirt-main-pool/ec6ccb14-03c2-49cc-9cc0-b1a87d582ed7/images/4081ce8f-1ce1-4ee1-aa43-69af2dfc5ab6/f8066c56-6db1-4605-8d7c-0739335d30b8.lease', offset=0) for host id 2 (clusterlock:424)
2020-01-09 05:27:14,498-0600 INFO  (tasks/4) [storage.VolumeManifest] Volume: preparing volume 6e627364-5e0c-4250-ac95-7cd914d0175f/f8066c56-6db1-4605-8d7c-0739335d30b8 (volume:569)
2020-01-09 05:27:14,502-0600 INFO  (tasks/4) [storage.SANLock] Releasing Lease(name='f8066c56-6db1-4605-8d7c-0739335d30b8', path=u'/rhev/data-center/mnt/192.168.2.223:_mnt_ovirt-main-pool/ec6ccb14-03c2-49cc-9cc0-b1a87d582ed7/images/4081ce8f-1ce1-4ee1-aa43-69af2dfc5ab6/f8066c56-6db1-4605-8d7c-0739335d30b8.lease', offset=0) (clusterlock:487)
2020-01-09 05:27:14,504-0600 INFO  (tasks/4) [storage.SANLock] Successfully released Lease(name='f8066c56-6db1-4605-8d7c-0739335d30b8', path=u'/rhev/data-center/mnt/192.168.2.223:_mnt_ovirt-main-pool/ec6ccb14-03c2-49cc-9cc0-b1a87d582ed7/images/4081ce8f-1ce1-4ee1-aa43-69af2dfc5ab6/f8066c56-6db1-4605-8d7c-0739335d30b8.lease', offset=0) (clusterlock:496)
2020-01-09 05:27:14,504-0600 ERROR (tasks/4) [root] Job u'9a47a14f-d398-4fe8-81fa-59cba7122aa0' failed (jobs:221)
Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/vdsm/jobs.py", line 157, in run
    self._run()
  File "/usr/lib/python2.7/site-packages/vdsm/storage/sdm/api/copy_data.py", line 61, in _run
    with self._source.prepare(), self._dest.prepare():
  File "/usr/lib64/python2.7/contextlib.py", line 17, in __enter__
    return self.gen.next()
  File "/usr/lib/python2.7/site-packages/vdsm/storage/sdm/api/copy_data.py", line 172, in prepare
    self.volume.prepare(rw=self._writable, justme=False)
  File "/usr/lib/python2.7/site-packages/vdsm/storage/volume.py", line 574, in prepare
    raise se.prepareIllegalVolumeError(self.volUUID)
prepareIllegalVolumeError: Cannot prepare illegal volume: ('f8066c56-6db1-4605-8d7c-0739335d30b8',)
2020-01-09 05:27:14,505-0600 INFO  (tasks/4) [root] Job u'9a47a14f-d398-4fe8-81fa-59cba7122aa0' will be deleted in 3600 seconds (jobs:249)
2020-01-09 05:27:14,506-0600 INFO  (tasks/4) [storage.ThreadPool.WorkerThread] FINISH task f1504b2d-c6c2-4866-97ce-e0476b0ba9a2 (threadPool:210)
2020-01-09 05:27:16,459-0600 INFO  (jsonrpc/4) [api.host] START getJobs(job_type=u'storage', job_ids=[u'9a47a14f-d398-4fe8-81fa-59cba7122aa0']) from=::ffff:192.168.2.15,57858, flow_id=94ad3bf0-c5f5-4d45-af2a-49aa4eaa6731 (api:46)
2020-01-09 05:27:16,460-0600 INFO  (jsonrpc/4) [api.host] FINISH getJobs return={'status': {'message': 'Done', 'code': 0}, 'jobs': {u'9a47a14f-d398-4fe8-81fa-59cba7122aa0': {'status': 'failed', 'error': {'message': "Cannot prepare illegal volume: ('f8066c56-6db1-4605-8d7c-0739335d30b8',)", 'code': 227}, 'job_type': 'storage', 'id': u'9a47a14f-d398-4fe8-81fa-59cba7122aa0', 'description': 'copy_data'}}} from=::ffff:192.168.2.15,57858, flow_id=94ad3bf0-c5f5-4d45-af2a-49aa4eaa6731 (api:52)
2