Method 1: Back up the guest OS with backup software:
Backing up guest OS (on OS platforms supported by backup software):
Since the guest OS is running on a platform that is supported by backup software. Backing up the guest OS itself is only a matter of installing backup software and performing both file, and system state backup with settings of your choice. This is essentially the same as configuring backup on a physical machine.
Backing up guest OS (on OS platforms with database hosted):
If the database hosted on the guest OS is supported by backup software. Simply install backup software on the guest OS and perform file, system state, and database backup with the settings of your choice.
If the database hosted on the guest OS is not supported by backup software. Then to handle the backup of such database, please follow the instructions below:
- Use the pre/post backup command to shutdown and startup the applications before and after a backup job (assuming that the database or application does not need to be online 24x7 and the database file is small enough to be transmitted to the backup software server each night.
- Use the pre-backup command to run a database specific command to export all database data to a dump file and upload this dump file using a file-type backup set.
Considerations: While this technique is straightforward to implement, there are several disadvantages.
- System restores can be problematic with this backup methodology.
- Furthermore, backup processing load needs to be taken into consideration as well. We would recommend that each individual guest OS be backed up one at a time to minimize the impact that backup might have on other guest OS hosted on the same VMware server.
Method 2: Back up the VMware disk (vmdk) files:
Each VMware guest OS has at least one physical disk file associated with it. VMware places these files on top of VMFS and adds a "vmdk" extension to each file. These files can be backed up using a file-type backup set. In this configuration, backup software is installed on the VMware server console or VMware Consolidated Backup (VCB) proxy server. Restoration of a virtual machine would simply require the restoration of the individual vmdk file(s) associated with that virtual machine.
To ensure files that are backed up are not corrupt, all I/O operations to these files must be halted prior to the backup operation. There are three ways to accomplish this:
- Shutdown or suspend the virtual machine. I/O operations to the vmdk files must be halted, and powering off the guest OS is probably the simplest way of accomplishing that. Unfortunately, with this technique, the virtual machine will be unavailable for the duration of the backup.
- Create a snapshot of the virtual machine. This technique utilizes the snapshot module (VCBMounter.exe) built into ESX Server. While the virtual machine is operating, ESX Server can halt all I/O operations to the vmdk files by invoking vcbmounter with commandline. All I/O operation to the vmdk files are halted, and new I/O operations are captured by a Redo log(s).
With this technique, the virtual machine is always available for the duration of the backup. Once the backup is completed, Redo log(s) is applied to the corresponding vmdk files and the Redo log will be removed afterward. This technique must be used carefully, as the VCBMounter.exe snapshot technology leaves the backed up guest OS and applications based on vmdk files in a "crash consistent" form. There is no guarantee that a restore from this condition will be usable (http://www.vmware.com/pdf/esx_backup_wp.pdf). Thus, we would not recommend using this technique.
- Shutdown the virtual machine, then create a snapshot. In this technique the virtual machine is powered off, a snapshot is quickly created, the machine is powered on, and then the backup proceed. This technique provides a compromise backup methodology that limits the downtime of the virtual machine while assuring that the virtual machine backed up is recoverable.
Considerations: Backing up the vmdk files associated with the virtual machines is straightforward and provides certain advantages and limitations. They include:
- If each virtual machine located on a single physical machine is backed up, it is recommended to limit the number of file systems that are backed up in parallel, to minimize the I/O impact that backup operations might have on running virtual machines.
- All vmdk files associated with a specific virtual machine must be backed up at the same time. If the vmdk files are not backed up at the same point in time, data loss or corruption can occur. It is also required that the VMware configuration files catalog, unmount.dat, .log, .nvram and .vmx files be backed up as well. These files are small and are rarely updated, but it is required that they be backed up each time the guest OS vmdk files are backed up.