Corral virtual server backup

VMware backups
When backing up a VMware machine, you have to back up the operating system of the VMware server (known as the service console on ESX systems) and the VMware application itself. You also need to back up each virtual machine's files. However, you cannot simply back up the virtual machine files or raw disks with a standard backup program. The virtual disks are constantly open and changing while the virtual machines are running and you will not receive a consistent backup of them. Even open file agents won't necessarily work properly if the virtual machines are gigabytes in size. You therefore have three options for backing up virtual machines running inside VMware:

  • Back up virtual machines as physical machines.
  • Back up virtual files while virtual machines are suspended.
  • Use VMware's built-in tools to copy a running virtual machine's files.

Back up virtual machines as physical machines
This is, of course, the easy method. Simply pretend that each virtual machine is a physical machine, and back it up as such. This method has both advantages and disadvantages.

Tip: If you use this method, don't forget to exclude the virtual machine files when you're

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backing up the VMware Server or ESX service console.

The first advantage of this method is that you can use the same backup system as the rest of your data center. Just because the machines are virtual doesn't mean you have to treat them as such. This simplifies your backup system. It also allows you to take advantage of full and incremental backups. Unless your backup software is able to perform subfile incremental backups, the other two methods perform full backups every day because the entire virtual machine is represented by a single file that will certainly change every day. Finally, it allows you to back up the systems live.

The disadvantage is that you have to configure backups for each virtual machine. Some may prefer to configure one backup for the entire VMware server. If you're using a commercial backup software package, this also increases your cost because you must buy a license for each virtual machine. A final disadvantage is that you also need to configure a bare-metal recovery backup for each virtual machine. Each of the other two methods won't need such a backup because restoring the virtual machine is all that's needed to perform its bare-metal recovery.

Back up suspended virtual machine files
If you can afford the downtime for each virtual machine, all you have to do is suspend a virtual machine prior to backing up its files. You can then back up the virtual machine files using your favorite backup program because the files won't be open or changing during your backup. The suspend function in VMware works just the same as on your laptop (and some servers). The current memory image and running processes are saved to a file that is then accessed when you power it on, causing all running processes to resume where they left off just before you suspended the machine.

This was first published in June 2007

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