客户问题概括:

客户在2008R2 Hyper-V 主机上用自带Windows Server Backup 备份时出现错误无法备份，在Hyper-V主机上发现如下日志.

Log Name: Microsoft-Windows-Backup
Source: Microsoft-Windows-Backup
Date: 2/5/2015 00:00:22 AM
Event ID: 9
Task Category: None
Level: Error
Keywords:
User: SYSTEM
Computer: HV01
Description:
The backup operation that started at '‎2011‎-‎2‎-‎5:' has failed because the Volume Shadow Copy Service operation to create a shadow copy of the volumes being backed up failed with following error code '0x80780021'. Please review the event details for a solution, and then rerun the backup operation once the issue is resolved

查找到已有MS博客描述类似问题，在遵循其方法后问题依然存在，已进行如下修改:
在注册表:
HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\SPP
创建新DWORD值命名为"CreateTimeout",值为12000000.

发现博主可能忽略其他一些相关操作，在进行上述注册表操作后要进行以下操作:

重启 BITS, VSS 和Com+ event system 服务，注意BITS服务重启会中断系统更新等依赖服务.

参考MS博客:
Windows Server Backup failed to backup with error 0x81000101
https://blogs.technet.microsoft.com/asiasupp/2011/08/01/windows-server-backup-failed-to-backup-with-error-0x81000101/