What Is Application-Consistent Backup?

Overview

There are three backup types in terms of backup consistency:

Inconsistent backup: Files in an inconsistent backup contain data taken from different points in time. This typically occurs if changes are made to your files or the data on your disks while backup is running. CBR cloud server backup uses the consistency snapshot technology for disks to protect data of ECSs. If you back up multiple EVS disks separately, the backup time points of the EVS disks are different. As a result, the backup data of the EVS disks is inconsistent.
Crash-consistent backup: A crash-consistent backup captures data that exists on disks as of the backup time, without backing up memory data or quiescing application systems. Backup consistency of application systems is not ensured. To complete this, disks are checked upon operating system restart to restore damaged data, for example, by using chkdsk, and log rollback is performed on databases to keep data consistent.
Application-consistent backup: An application-consistent backup is a backup of application data that allows applications to achieve a quiescent and consistent state. This type of backup captures the contents of the memory and any pending writes that occurred during the backup process.

Figure 1 compares these backup types in detail.

CBR supports both crash-consistent backup and application-consistent backup (also called database server backup).

If a MySQL or SAP HANA database is deployed on a server, you can use CBR application-consistent backup to back up the server data and application cache. Crash-consistent backup backs up only data and some application caches without interrupting services. If a system fails or data loss occurs, you can use an application-consistent backup to quickly restart services. A crash-consistent backup, however, may fail to restore some application configurations.

Figure 1 Backup consistency

Differences Between Application-Consistent Backup Cloud Server Backup

Item	Application-Consistent Backup	Cloud Server Backup
Backup and restore object	Cloud servers with MySQL or SAP HANA database deployed	Cloud servers excluding database applications
Backup unit	Cloud server	Cloud server
Vault type	Server backup vault	Server backup vault
Recommended scenario	Data of cloud servers as well as their deployed databases, such as MySQL or SAP HANA database needs to be backed up. All data and application configurations need to be restored in case of an error.	Only data of cloud servers needs to be backed up. All data needs to be restored in case of an error. In the event that a cloud server backup is performed for a server deployed with a MySQL or SAP HANA database, if the backup is then used to restore data, some database configurations may fail to be restored, and issues may occur after the database is restarted.

Application Scope

Table 1 lists the OSs that support the installation of Agent.

**Table 1** OSs that support installation of the Agent
Database	OS	Version
SQL Server 2008/2012	Windows	Windows Server 2008, 2008 R2, 2012, and 2012 R2 for x86_64
SQL Server 2014/2016/EE	Windows	Windows Server 2014, 2014 R2, and 2016 Datacenter for x86_64
MySQL 5.5/5.6/5.7	Red Hat	Red Hat Enterprise Linux 6 and 7 for x86_64
	SUSE	SUSE Linux Enterprise Server 11 and 12 for x86_64
	CentOS	CentOS 6 and 7 for x86_64
	EulerOS	EulerOS 2.2 and 2.3 for x86_64
HANA 1.0/2.0	SUSE	SUSE Linux Enterprise Server 12 for x86_64

For the databases not included in this list, you can customize a script to perform application-consistent backup by referring to section "Using a Custom Script to Implement Application-Consistent Backup" in the Cloud Backup and Recovery Best Practices.

Process

Figure 2 shows the application-consistent backup process.

Figure 2 Application-consistent backup process

Change the security group: Before performing an application-consistent backup task, change the security group of the server you want to back up. For details, see Changing a Security Group.
Install the agent: Change the security group and install the agent in any sequence. Ensure that the two operations are completed before backing up the desired server. For details, see Installing the Agent.
Create an application-consistent backup: After creating a server backup vault for storing application-consistent backups, associate it with the desired database server and then create an application-consistent backup. For details, see Creating an Application-Consistent Backup.
Modify or compile a custom script: After backing up a database server on CBR Console, modify or compile a custom script on the database of the server. For details, see Best Practices.
Verify the backup result: After the backup is performed, verify that the backup succeeds. For details, see Best Practices.
Use the backup to restore server data: Use the application-consistent backup to restore server data. The restored database applications and data are the same as those at the backup point in time. For details, see Restoring Data Using a Cloud Server Backup.