如何判断备份日志链是否损坏？

Question

如何判断备份日志链是否损坏？

San*_* KB 8 sql-server backup

我遇到过在服务器上进行本机备份的情况。
我碰巧看到msdb有一个第三方备份工具 ( AppAssure) 也在使用 VSS (kind-of) backup to virtual device。

在某个时间间隔内，AppAssure（对进行备份VIRTUAL DEVICE）正在执行 a，COPY_ONLY backup而在其他时间间隔内，它正在FULL backup破坏日志链。

有没有办法（T-SQL query）知道备份日志链何时被破坏？

这是2月份情况的屏幕截图。

Answer 1

Joh*_* N. 9

参考阅读/类似问答

您可能想查看我针对以下问题发布的答案： VSS 备份会破坏日志链吗？(dba.stackexchange.com)

我的回答中的解释还链接到如何使用 Windows Server Backup 备份 SQL Server 数据库的问题？（serverfault.com）这也是我自己回答的。

交易日志链

执行事务日志 (TLOG) 备份时，备份信息存储在msdb数据库中的各个表中。存储将包含像信息的信息backup_type，logical_device_name，physical_device_name，is_copy_only，is_snapshot，和各种..._lsn柱（LSN =日志序列号）。

您可以使用以下脚本通过 msdb 数据库从 SQL Server 实例中检索事务日志备份链信息：

/* ==================================================================
 Author......:  hot2use 
 Date........:  25.04.2018
 Version.....:  0.1
 Server......:  localhost (first created for)
 Database....:  msdb
 Owner.......:  -
 Table.......:  various
 Type........:  Script
 Name........:  ADMIN_Retrieve_Backup_History_Information.sql
 Description.:  Retrieve backup history information from msdb database
 ............   
 ............   
 ............       
 History.....:   0.1    h2u First created
 ............       
 ............       
================================================================== */
SELECT /* Columns for retrieving information */
       -- CONVERT(CHAR(100), SERVERPROPERTY('Servername')) AS SRVNAME, 
       msdb.dbo.backupset.database_name,
       msdb.dbo.backupset.backup_start_date,
       msdb.dbo.backupset.backup_finish_date,
       -- msdb.dbo.backupset.expiration_date, 

       CASE msdb.dbo.backupset.type
            WHEN 'D' THEN 'Full'
            WHEN 'I' THEN 'Diff'
            WHEN 'L' THEN 'Log'
       END  AS backup_type,
       -- msdb.dbo.backupset.backup_size / 1024 / 1024 as [backup_size MB],  
       msdb.dbo.backupmediafamily.logical_device_name,
       msdb.dbo.backupmediafamily.physical_device_name,
       -- msdb.dbo.backupset.name AS backupset_name,
       -- msdb.dbo.backupset.description,
       msdb.dbo.backupset.is_copy_only,
       msdb.dbo.backupset.is_snapshot,
       msdb.dbo.backupset.checkpoint_lsn,
       msdb.dbo.backupset.database_backup_lsn,
       msdb.dbo.backupset.differential_base_lsn,
       msdb.dbo.backupset.first_lsn,
       msdb.dbo.backupset.fork_point_lsn,
       msdb.dbo.backupset.last_lsn
FROM   msdb.dbo.backupmediafamily
       INNER JOIN msdb.dbo.backupset
            ON  msdb.dbo.backupmediafamily.media_set_id = msdb.dbo.backupset.media_set_id 

        /* ----------------------------------------------------------------------------
        Generic WHERE statement to simplify selection of more WHEREs    
        -------------------------------------------------------------------------------*/
WHERE  1 = 1

       /* ----------------------------------------------------------------------------
       WHERE statement to find Device Backups with '{' and date n days back
       ------------------------------------------------------------------------------- */
       -- AND     physical_device_name LIKE '{%'

       /* -------------------------------------------------------------------------------
       WHERE statement to find Backups saved in standard directories, msdb.dbo.backupfile AS b 
       ---------------------------------------------------------------------------------- */
       -- AND     physical_device_name  LIKE '[fF]:%'                          -- STANDARD F: Backup Directory
       -- AND     physical_device_name  NOT LIKE '[nN]:%'                      -- STANDARD N: Backup Directory

       -- AND     physical_device_name  NOT LIKE '{%'                          -- Outstanding Analysis
       -- AND     physical_device_name  NOT LIKE '%$\Sharepoint$\%' ESCAPE '$' -- Sharepoint Backs up to Share
       -- AND     backupset_name NOT LIKE '%Galaxy%'                           -- CommVault Sympana Backup


       /* -------------------------------------------------------------------------------
       WHERE Statement to find backup information for a certain period of time, msdb.dbo.backupset AS b 
       ---------------------------------------------------------------------------------- 
       AND    (CONVERT(datetime, msdb.dbo.backupset.backup_start_date, 102) >= GETDATE() - 7)  -- 7 days old or younger
       AND    (CONVERT(datetime, msdb.dbo.backupset.backup_start_date, 102) <= GETDATE())  -- n days old or older

       */

       /* -------------------------------------------------------------------------------
       WHERE Statement to find backup information for (a) given database(s) 
       ---------------------------------------------------------------------------------- */
       AND database_name IN ('AdventureWorks2012') -- database names
       -- AND     database_name IN ('rtc')  -- database names

        /* -------------------------------------------------------------------------------
        ORDER Clause for other statements
        ---------------------------------------------------------------------------------- */
        --ORDER BY        msdb.dbo.backupset.database_name, msdb.dbo.backupset.backup_finish_date -- order clause

        ---WHERE msdb..backupset.type = 'I' OR  msdb..backupset.type = 'D'
ORDER BY
       --2,

       2       DESC,
       3       DESC

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^{注意： where 子句当前选择 AdventureWorks2012 数据库}

中断的事务日志链

除非满足以下条件之一，否则（事务）日志链永远不会中断：

事务日志备份文件被删除
无法访问事务日志备份文件（备份设备中的某处；第 3 方备份解决方案）
数据库处于 SIMPLE 恢复模式
使用选项执行了事务日志备份 TRUNCATE_ONLY
a FULL Database backup was taken without the COPY_ONLY option and was then deleted from disk because the developers only needed a quick backup to analyse a situation in the database and your FULL backup before that was deleted by (a) backup procedure.

Your Situation

In the screenshot you provided you have a FULL backup of the database that is is_copy_only and shortly after a FULL backup that is not is_copy_only. Now what you don't know:

Is the second FULL, non-is_copy_only backup a snapshot or not?

If you use my script from above and change the WHERE clause to match your database name, you might find out that that FULL backup that is not is_copy_only might just be a is_snapshot.

And that might just open up a new question:

Will the FULL, is_snapshot database backup of my database break the log backup chain?

But...

....whichever way this goes, as long as you have an unbroken chain of FULL and TLOG backups you can access, you can still restore your database to any point in time, even if you have another FULL backup in-between.

You can verify this with the output of my script for your database, by looking at the first_lsn and last_lsn numbers. They should match up, even when bypassing a FULL backup.

Better Be Safe Than Sorry

I have an AdminDB2 database on one of my instances. I created a TLOG backup, modified data, performed a FULL backup, modified data, performed a TLOG backup, ....

Lets have a look at my backup history of my AdminDB2:

dbname    backup_start_date       backup_finish_date            type    Log   physical_device_name                                          C   S   checkpoint_lsn   dbase_backup_lsn     dlsn  first_lsn           flsn    last_lsn
AdminDB2    2018-04-25 17:29:08.000 2018-04-25 17:29:08.000 TLOG    NULL    C:\SQL\Backup\AdminDB2\TLOG\AdminDB2_TLOG_20180425_172908.trn   0   0   36000002022400042   36000002022400042   NULL    36000002021900001   NULL    36000002025100001
AdminDB2    2018-04-25 17:28:48.000 2018-04-25 17:28:48.000 Full    NULL    C:\SQL\Backup\AdminDB2\FULL\AdminDB2_FULL_20180425_172848.bak   0   0   36000002022400042   36000002018900037   NULL    36000002022400042   NULL    36000002024200001
AdminDB2    2018-04-25 17:28:23.000 2018-04-25 17:28:23.000 TLOG    NULL    C:\SQL\Backup\AdminDB2\TLOG\AdminDB2_TLOG_20180425_172823.trn   0   0   36000002018900037   36000002018900037   NULL    36000002021500001   NULL    36000002021900001
AdminDB2    2018-04-25 17:28:07.000 2018-04-25 17:28:07.000 TLOG    NULL    C:\SQL\Backup\AdminDB2\TLOG\AdminDB2_TLOG_20180425_172807.trn   0   0   36000002018900037   36000002018900037   NULL    36000002018400001   NULL    36000002021500001
AdminDB2    2018-04-25 17:27:32.000 2018-04-25 17:27:32.000 Full    NULL    C:\SQL\Backup\AdminDB2\FULL\AdminDB2_FULL_20180425_172732.bak   0   0   36000002018900037   36000001990800037   NULL    36000002018900037   NULL    36000002020600001
AdminDB2    2018-04-25 17:15:00.000 2018-04-25 17:15:00.000 TLOG    NULL    C:\SQL\Backup\AdminDB2\TLOG\AdminDB2_TLOG_20180425_171500.trn   0   0   36000002016000003   36000001990800037   NULL    36000002018100001   NULL    36000002018400001

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_{The order is date descending}

You can see the last TLOG backup at the top, the previous FULL (in-between) backup at 2018-04-25 17:28:48.000, the previous TLOG backup at 2018-04-25 17:28:23.000, and so on.

To restore the AdminDB2 database to the current point-in-time I would have to use the first FULL backup from 2018-04-25 17:27:32.000 (because I deleted the in-between FULL backup) together with all the TLOG backups.

Let's give that a try.

Delete the FULL backup file AdminDB2_FULL_20180425_172848.bak on my disk (or rename it), just because it is the one in-between.
Open up the Restore GUI in SSMS and add ..
- the FULL backup AdminDB2_FULL_20180425_172732.bak
- all the TLOG backup files
  - AdminDB2_TLOG_20180425_172807.trn
  - AdminDB2_TLOG_20180425_172823.trn
  - AdminDB2_TLOG_20180425_172908.trn
Make sure i set the option Overwrite the existing database (WITH REPLACE)
Perform the restore (or script the statement out into a query window)

Script

USE [master]
RESTORE DATABASE [AdminDB2] FROM  DISK = N'C:\SQL\BACKUP\AdminDB2\FULL\AdminDB2_FULL_20180425_172732.bak' WITH  FILE = 1,  NORECOVERY,  NOUNLOAD,  STATS = 5, REPLACE
RESTORE LOG [AdminDB2] FROM  DISK = N'C:\SQL\BACKUP\AdminDB2\LOG\AdminDB2_LOG_20180425_172807.trn' WITH  FILE = 1,  NORECOVERY,  NOUNLOAD,  STATS = 5
RESTORE LOG [AdminDB2] FROM  DISK = N'C:\SQL\BACKUP\AdminDB2\LOG\AdminDB2_LOG_20180425_172823.trn' WITH  FILE = 1,  NORECOVERY,  NOUNLOAD,  STATS = 5
RESTORE LOG [AdminDB2] FROM  DISK = N'C:\SQL\BACKUP\AdminDB2\LOG\AdminDB2_LOG_20180425_172908.trn' WITH  FILE = 1,  NOUNLOAD,  STATS = 5

GO

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Output

15 percent processed.
30 percent processed.
45 percent processed.
60 percent processed.
75 percent processed.
90 percent processed.
100 percent processed.
Processed 848 pages for database 'AdminDB2', file 'AdminDB' on file 1.
Processed 2 pages for database 'AdminDB2', file 'AdminDB_log' on file 1.
RESTORE DATABASE successfully processed 850 pages in 0.134 seconds (49.502 MB/sec).
100 percent processed.
Processed 0 pages for database 'AdminDB2', file 'AdminDB' on file 1.
Processed 2 pages for database 'AdminDB2', file 'AdminDB_log' on file 1.
RESTORE LOG successfully processed 2 pages in 0.005 seconds (3.027 MB/sec).
100 percent processed.
Processed 0 pages for database 'AdminDB2', file 'AdminDB' on file 1.
Processed 1 pages for database 'AdminDB2', file 'AdminDB_log' on file 1.
RESTORE LOG successfully processed 1 pages in 0.005 seconds (0.390 MB/sec).
100 percent processed.
Processed 0 pages for database 'AdminDB2', file 'AdminDB' on file 1.
Processed 2 pages for database 'AdminDB2', file 'AdminDB_log' on file 1.
RESTORE LOG successfully processed 2 pages in 0.005 seconds (3.125 MB/sec).

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...and the database is back ONLINE.

Summary

The backup chain only breaks when you lose the TLOG backups in-between, other than that you can restore a database from a FULL backup a long time ago and just add all the TLOG backups.

However...

...it is faster to have a more recent FULL, DIFF and TLOG backups handy.

_{Additional information in response to comment: Transaction Log backup was performed with the option TRUNCATE_ONLY - when this happens, is there any way to know this by T-SQL query}

Backing Up Transaction Log With Truncate_only

In previous versions of SQL Server prior to SQL Server 2008 you could use the following statement:

 BACKUP LOG [AdminDB2] WITH TRUNCATE_ONLY

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This has been deprecated and is no longer supported. You will receive an error message like the following:

Msg 155, Level 15, State 1, Line 10
'TRUNCATE_ONLY' is not a recognized BACKUP option.

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The new method is to backup to disk NUL and is performed with the following command:

BACKUP LOG [AdminDB2] TO DISK='NUL'

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This will return the following information:

Processed 1 pages for database 'AdminDB2', file 'AdminDB_log' on file 1.
BACKUP LOG successfully processed 1 pages in 0.001 seconds (1.464 MB/sec).

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Advisory
Do NOT use this in production. You will lose the ability to restore to a point-in-time during that TLOG backup.

Reference: BACKUP (Transact-SQL) (Microsoft Docs)

Your backup history will show this as:

dbname      backup_start_date       backup_finish_date      type ldev  pdev C   S   checkpoint_lsn   dbase_backup_lsn     dlsn  first_lsn           flsn    last_lsn
AdminDB2    2018-04-26 09:35:05.000 2018-04-26 09:35:05.000 Log NULL    NUL 0   0   36000002030100002   36000002022400042   NULL    36000002033400001   NULL    36000002033700001

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The information for the logical_device_name (ldev) and physical_device_name (pdev) will both contain the value NULL. This is a sign that a BACKUP LOG ... was performed with a TRUNCATE_ONLY (new: TO DISK='NUL'). You will have lost the ability to restore past this point using Transaction Log backups.

_{Additional information in response to comment: Yes - this was a is_snapshot = 1 [backup]}

is_snapshot

Please read the section is_snapshot in my answer to the question Use of third-party VSS backup plus native SQL backup

From my original answer:

If the database backup history has the flag is_snapshot set to 1 then you know that this backup was performed using a 3rd-party software that triggered the SQL Server Writer (VSS Service for SQL Server) which allowed the 3rd-party software to backup the database almost instantaneously.

From the official documentation on what Snapshot Backups are:

SQL Server snapshot backup is accomplished in cooperation with third-party hardware or software vendors, or both. These vendors use SQL Server features that are designed for this purpose. The underlying backup technology creates an instantaneous copy of the data that is being backed up. The instantaneous copying is typically accomplished by splitting a mirrored set of disks or by creating a copy of a disk block when it is written. This preserves the original. At restore time, the original is made available immediately and synchronization of the underlying disks occurs in the background. This results in almost instantaneous restore operations.

Reference: Snapshot Backups (Microsoft Technet)

A backup created using this feature can also be restored almost instantaneously.

Summary

第 3 方备份应标记为is_snapshot = 1和is_copy_only = 1。这些备份不会与其他备份步骤冲突/程序使用本地SQL Server执行的BACKUP DATABASE...，BACKUP DATABASE ... WITH DIFFERENTIAL....和BACKUP LOG...语句。第 3 方数据库备份不是现有备份集的一部分。

我希望这些信息是足够的。

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