I have several working VADP client backups and they seem to be rather stable. If they start to work, then they usually work all the time.

But then I have a couple of VADP backup clients, that just doesn't seem to work. There seems to be two different scenarios, these are both Windows 2003 SP2 servers, but I think the first problem also was on a 2008 R2 :

1. The snapshot is created, but when the VADP proxy is trying to "Download the VM configuration for [client]" it fails with following errors:

* :guest/client:*FULL* 2011-06-07T10:52:33Z SnapShot created Successfully for VM 'guest/client'.
* :guest/client.*FULL* Downloading VM configuration for guest/client.
* :guest/client.*FULL* 2011-06-07T10:54:36Z 83065:nsrvadp_save: The following internal error occurred: libcurl error: Timeout was reached
* :guest/client.*FULL* 83687:nsrvadp_save: Could not download VM configuration for VM 'guest/client'.
* :guest/client.*FULL* 2011-06-07T10:54:36Z Temporary directory 'D:\\VADP\guest/client' for VADP deleted.

Sometimes it leaves the snapshot, sometimes not. There are no errors in the vCenter to be found. Nothing in the guest itself either.

2. The creating of the snapshot is failed because of "Cannot create a quiesced snapshot because the create snapshot operation exceeded the time limit for holding off I/O in the frozen virtual machine." This is the whole output from the log:

* :guest/client.*FULL* 2011-06-07T10:48:56Z Creating snapshot for 'vm-36481' ...
* :guest/client.*FULL*  Task is -1% complete
* :guest/client.*FULL* 2011-06-07T10:49:04Z  Task is 95% complete
* :guest/client.*FULL* 2011-06-07T10:49:11Z 74854:nsrvadp_save: The following VMware related error occured: Unable to create snapshot '_VADP-BACKUP_' for VM: vm-36481.  Details: 'An error occurred for task 'CreateSnapshot_Task'.  Details: Cannot create a quiesced snapshot because the create snapshot operation exceeded the time limit for holding off I/O in the frozen virtual machine.'.
* :guest/client.*FULL* 80405:nsrvadp_save: Could not create Snapshot for VM 'guest/client.
* :guest/client.*FULL* 2011-06-07T10:49:11Z Temporary directory 'D:\\VADP\guest/client' for VADP deleted.

The same error message can be found in the vCenter, but if I take a quiesced snapshot manually from this client it works ok. I have googled around and this has possibly something to do with VSS, because in the event log on the guest i found these errors

Source: VSS

Event ID: 8193

Volume Shadow Copy Service error: Unexpected error calling routine RegSaveKeyExW.  hr = 0x800703f8.

But I haven't found anything wrong with VSS, vssadmin list writers outputs what is expected.

A workaround for this would be to take a nonquiesced snapshot, but even though there was a way to do it with the old VCB backup, I haven't found a way to do it with VADP. Another workaround is to install vmware tools without VSS support, but I don't want to do that. because I sometimes want a quiesced snapshot taken manually.