I get a lot of event 157 (Disk X has been surprise removed.) in the event log on my Veeam Backup server (Windows Server 2012 R2) during backup jobs. Why is this happening?
Yes, I suppose so, but not deliberately. The backup server is virtual and located on a host with local storage. The backup server is backing up VMs located both on the same host and on other hosts. There is no SAN involved, just local storage. The action logs say that "hotadd" is used on the VMs located on the same host, otherwise "nbd". Does Veeam Backup release the hotadded disks improperly?
Yes, I have searched through all logs from the last backups session. I can see that this error is always logged by Veeam Backup one second before event 157 is written to the Windows event log.
That may explain the Windows log event, but why is Veeam logging an error while trying to remove the device? It doesn't look like expected behavior. I have to admit that the hotadd feature feels a bit unreliable. Is it possible to disable hotadd in Veeam Backup?
This error comes from vSphere, when it detaches disk from the proxy server (Veeam B&R just translates vSphere logs for operations, where it calls vSphere to do something). So this is internal to VMware and tells nothing against hotadd reliability and overall Veeam B&R operation. You can trust hotadd, since it's proved its reliability over all 8 previous versions of Veeam B&R. Besides, as you can see from the provided link, the same occurs in case of Hyper-V.
I'm seeing this behavior too. I checked Disk Management during a backup and it appears that Veeam mounts the VMDK files as offline disks to back them up. This error seems to appear in the event log when it disconnects the disk.
Is that an accurate representation? That is, Veeam does mount the VMDK files for a given VM during a backup?
As an aside, I use the term 'error' loosely. In reality, it's a warning, not an error. I'm happy to ignore warnings assuming my observations above are expected behavior.