1. Backing Up the System Databases
You need to make sure you
include the system databases as a part of your backup strategy. If you
have to rebuild a server, you will be able to use the system database
backups to restore any custom configurations, including jobs, logins,
and so on. We generally include the system databases in a full daily
backup routine and take special one-off backups after certain
information in the database changes.
Following are the system databases and some things that you need to know about backing them up:
master: The master database uses the simple recovery model, and you can only perform full database backups of the master database. You should back up this database whenever certain operations cause it to be updated, including the following:
Adding and removing user databases
Adding and removing logins
Adding and removing a backup device
Adding and removing linked servers and remote logins
Modifying metadata for user databases, such as file locations or adding and removing filegroups
msdb: The msdb
database uses the simple recovery model by default, but it can be
configured to use any recovery model. For example, you can change the
recovery model of the msdb to full
and take advantage of transaction log backups if you are highly
dependent on information that is stored in this database. The
information in the msdb database changes
often because it logs historical information for items like backups, SQL
Agent jobs, and database mail. At minimum, you should take a full
backup of the msdb after making configuration changes, including the following:
Adding and removing SQL Agent jobs
Adding and removing maintenance plans
Importing SSIS packages
Adding and removing Policies and central management servers
Configuring log shipping
Configuring database mail
Configuring operators and alerts
model:
This database uses the full recovery model by default, but it can be
configured to use any recovery model. Remember, since the model database serves as a template for all new user databases, if you change the recovery model in the model
database, any newly created databases will be created with this
recovery model as well. You only need to perform full database backups
of the model database whenever you
make custom configuration changes. Even though the recovery model is set
to full, there is no activity in the model database to warrant transaction log backups.
tempdb: The recovery model for the tempdb is simple and cannot be changed. Every time you restart SQL Server, the tempdb
is recreated, and any data stored in it is lost. Since the tempdb is
recreated every time SQL Server is restarted, you are not allowed to
perform any type of backup operations on it.
Resource: This is a read-only database and is not visible in SQL Server Management Studio. The Resource database is only updated whenever service packs are applied to SQL Server. You cannot back up the Resource
database using a SQL Server backup operation. To backup this database,
you must perform a file-based backup operation by copying the
mssqlsystemresource.mdf file to your backup location. Unlike other data
files, you do not have to stop the SQL Server service in order to copy
the Resource data files.
2. Backup History
SQL Server maintains a set of tables that hold the backup history that is performed on each server instance in the msdb
database. You can use these tables to gather useful information, such
as the last time a backup was performed on each database. The backup
history tables include the following:
backupfile: Contains information about the data and log files for a database backup.
backupfilegroup: Contains information about every filegroup in a database when the backup was performed.
backupmediafamily: Holds one row for each media family, including the logical device name, physical device name, and device type.
backupmediaset: Holds one row for each backup media set. Each media set can have multiple media families.
backupset:
Holds a single row for each backup set created by a successful backup
operation. The backupset table holds information like the database name,
the backup start and end times, and log sequence numbers at the time of
backup.
After a while of capturing
backup information, the backup history tables can become rather large
depending on the number and frequency of backups performed. We have seen
the msdb grow to a fairly substantial size because of the amount of data stored in the backup history tables. Microsoft provides the sp_delete_backuphistory system stored procedure that you can use to limit the amount of history stored in these tables. The sp_delete_backuphistory
procedure enables you to enter a date/time parameter that will remove
all data created before a certain date or time. For example, the
statement Exec msdb.dbo.sp_delete_backuphistory '1/1/2009' will remove all the records from the backup history tables in the mdsb that were created before January 1, 2009.
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If your msdb database
already contains a lot of data in the history tables, it is best to
delete the data for smaller date ranges and test the impact on the
server instead of trying to remove several months or years all at once.
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Listing 1
shows a script you can use to keep a specified amount of history in the
database without deleting all of the history at once. If you have a lot
of history in your backup tables, you should start deleting the data in
smaller chunks until you see the impact that removing the data has on
your server. We maintain six months of history and never delete more
than three months of history each time the script is executed. Let's say
you schedule this script to run once a week. Every week you will delete
three months of history until you eventually delete all the backup data
you have built up prior to implementing this script and only have to
delete a single week of backup history.
Example 1. Script to Remove Backup History in the msdb in Three-Month Intervals While Maintaining Six Months of History
USE msdb
GO
--Keep 6 months of history, but never delete more than 3 months at a time.
Declare @dte Datetime
SET @dte = (SELECT MIN(backup_start_date) FROM backupset WITH (nolock))
SET @dte = (SELECT dateadd(mm,3,@dte))
IF (dateadd(mm,-6,getdate()) < @dte )
SET @dte = dateadd(mm,-6,getdate())
PRINT @dte
EXEC sp_delete_backuphistory @dte
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If you want to remove all the backup history for a specific database, you can execute the sp_delete_database_backuphistory system stored procedure followed by the database name. For example, the statement Exec msdb.dbo.sp_delete_database_backuphistory 'AdventureWorks2008' will remove all the records from the backup history tables in the msdb for the AdventureWorks2008 database.
