Forgot to write this down the first time, so here goes.
Steps I took to ensure writing to a Samba share worked:
Writing to an ext4 filesystem. smb.conf share level config: [sharename] browsable = no strict allocate = yes writable = yes create mask = 0700 directory mask = 0700 I had a directory owned by just the user drwx------ windows-backup within the share itself. I am pretty sure the key is "strict allocate = yes" to get rid of the message: The requested operation could not be completed due to a virtual disk system limitation. Virtual hard disk files must be uncompressed and unencrypted and must not be sparse. The operation ended before completion.