I/O is frozen on database, No user action is required
I recently responded to one of the questions in which the user wanted to know what these messages in the SQL Server Error Log mean.
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spid92,Unknown,I/O is frozen on database [databasename]. No user action is required. spid92,Unknown,I/O was resumed on database [databasename]. No user action is required. |
Even in my environment I have seen this message in some of the Data warehouse instances. This message is logged in the Error Log whenever any backup service making use of SQL Server Virtual Device Interface (VDI) tries to backup the database (with snapshot)/drive on which the database files reside. Microsoft Backup (ntbackup.exe), Volume Shadow Copy (VSS), Data Protection Manager (DPM) and third party tools like Symantec Business Continuance Volume (BCV) are some of the application which cause this message to logged in the SQL Server Error Log.
What does these messages mean? Let me explain this with an example. Suppose ntbackup.exe is configured to take the backup of D drive. This drive has some data files related to few databases on SQL Server. Since the data files are in use by SQL Server, if these files are copied as it is the files in the backup will be inconsistent. To ensure that the database files are consistent in the drive backup, this application internally issues a BACKUP DATABASE [databasename] WITH SNAPSHOT command against the database. When this command is issued, the I/O for that database is frozen and the backup application is informed to proceed with its operation. Until the BACKUP WITH SNAPSHOT command is complete, the I/O for the database is frozen and the I/O is resumed once it completes. The corresponding messages are logged in the SQL Server Error Log.
If the ntbackup is issued during business hours, the users accessing the database will surely have some connectivity issues. This is one of reasons why the backup on production systems should not be done during business hours. Like I mentioned earlier, in my environment I have seen these messages but during the regular downtime for backups.
数据库上的IO已冻结，不需要任何用户操作
我最近回复过的其中一个问题就是用户要了解在SQL Server错误日志中这些消息的意思。
spid92,Unknown,I/O is frozen on database [databasename]. No user action is required.
spid92,Unknown,I/O was resumed on database [databasename]. No user action is required.
甚至在我的环境中我也曾在数据仓库实例上看到过这条消息。这条消息记录在错误日志，当任何备份服务利用SQL Server虚拟设备接口（VDI）尝试备份数据库（with snapshot）/运行在数据库文件所在。 微软备份Backup(ntbackup.exe),卷影复制Volume Shadow Copy(VSS), 数据保护管理器Data Protection Manager(DPM)和第三方工作例如赛门铁克Symantec 业务连续性卷（Business Continuance Volume)(BCV)都是一些引起这条消息记录到SQL Server错误日志的应用程序。
那么这些消息是什么意思？ 让我用一个例子来解释下。 假设配置ntbackup.exe备份D盘。这个磁盘上有一些SQL Server上的数据库相关的数据文件。由于SQL Server要使用那些数据文件，因此如果这些文件在备份时复制将出现不一致。为了确保数据库文件在磁盘备份时是一致的，这些应用程序内部使用BACKUP DATABASE [数据库名称] WITH SNAPSHOT命令来备份数据库。当命令执行时，数据库上的I/O会冻结并且备份应用程序被通知继续进行起操作。直到BACKUP WITH SNAPSHOT命令执行完成，数据库的冻结的I/O当备份命令一旦完成就会恢复。相应的消息也就会记录到SQL Server错误日志中。
如果ntbackup在办公时间执行。访问数据库的用户将一定会遇到一些连接问题。这也就是为什么生产系统中的备份服务不在办公时间执行的原因之一。正如我先前所述，在我的环境中，我看到过这些消息不过都是在休息时间执行备份产生的。
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