I am having some issues running Windows backups to iSCSI drives. I have 7 Windows Servers (6 2008 R2, 1 2012 R2) running nightly backups to individual iSCSI LUNs/Targets on a Synology RS812+ (the iSCSI backup drives are the only use I have the Synology set up for at the moment). The backups do not always consistently complete successfully to the iSCSI drives and I am having a lot of trouble identifying why.
For example, last night only 4 of the 7 backups completed successfully. Of those 4 2 were VMs (on ESXi 5.5) and 2 were physical boxes (Dell Poweredges), of the 3 that failed 2 were VMs and 1 was a physical box. The error I receive from the failed backups is "Incorrect function" in the Windows Server Backup section of MMC and "The backup operation that started at '2014-06-20T13:12:48.697622700Z' has failed with following error code...