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Chapter 26: Log Shipping
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- Enter an amount of time that the server should wait to send an alert if no new
transaction log fi les are found. For example, if the server has not seen a transac-
tion log backup in the past 1 hour, then the Alert If No Backup Occurs Within
option should be set to 1 hour.
The longer the length of the alert time, the higher is the risk. With a long alert setting, a transaction log backup fail-
ure results in a larger amount of data loss.- Schedule the job that will back up the transaction log by setting the job’s name, time,
and frequency by clicking the Schedule button. A shorter duration between transac-
tion log backups minimizes the amount of data that could be lost. By default, the
transaction log is backed up every 15 minutes. The default works for most environ-
ments, but for some environments, setting the duration to 5 minutes is needed to
minimize data loss. The frequency of transaction log backups usually is determined by
a lot of factors such as SLAs, speed of your disk subsystem, and transaction log size.
Make sure that the only transaction log backup that occurs is scheduled through the Transaction Log Shipping page.
Otherwise, all the data changes will not be propagated to the secondary servers and log shipping will break.
If you have a powerful server with plenty of resources, you may be tempted to change the transaction log backup
frequency to every 1 minute or less. SQL Server 2012 lets you schedule the frequency to as little as every 10 sec-
onds. You may need this in your environment, but remember that this can create hundreds of transaction log back-
ups. If you have to restore your database using backups, then you have to restore the full database backup followed
by all the transaction log backups in order, and if one of the transaction log backups is bad, then the restore stops at
that point.- SQL Server 2012 Enterprise Edition supports backup compression. You can control
the backup compression by clicking the Set Backup Compression drop-down box on
the Transaction Log Backup Settings page. By default, Use the Default Server Setting
option is selected. This uses the default server level compression. You can bypass the
server level default by selecting the Compress Backup option, or you can choose not
to compress the backup by selecting the Do Not Compress Backup option.
The performance increase achieved from backup compression comes at the expense of CPU usage. If you have a CPU
bound SQL Server, then you may not want to compress the backup. It is recommended to do thorough testing to see
the impact of the backup compression because the CPU increase can impact other operations.- Add the secondary servers to the transaction log confi guration by clicking the Add
button under the secondary instance’s window. Multiple secondary instances can be
added here by repeating steps 9 through 16.
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