A common VMware Communities question is how to backup the VMware ESX virtualized server configuration so that it can be readily restored.

For disaster recovery and general good business sense it is important to make backups. But the most obvious way to make them—even for small shops—is not always the best.

The obvious choice is to back up the entire system file by file, or just the configuration files, specifically.

This approach doesn't work very well, however. You can't do a restoration onto bare metal using restoration disks and expect it to work. For one thing VMware ESX(i) VMs use unique IDs throughout an installation that will not be properly updated with a new ID during the restore. While it's an interesting management problem to have two servers with the same ID, VMware ESX(i) management tools tend to get very confused about this.

Making the restore work properly could also require quite a bit of manual labor and nearly identical hardware.

The next most-obvious backup choice is to reinstall ESX, then layer the configuration back onto the system by restoring specific files.

Unfortunately, that overwrites the unique IDs and leads to more confusion.

A similar approach is to restore the backup by hand, making all the necessary changes following the old configuration files. However, this would be time consuming at best.

The best backup choice is to make an automated installation CDROM that will automatically configure ESX for the hardware with all the appropriate configurations necessary.

This is called a kickstart install, which requires a post- installation script to be written that will perform all these tasks for you.

All but one task can be done from this kickstart script, and that is the addition of the server into virtual center. However, it can install VMware ESX(i), make all the necessary configuration changes, update licenses, and install any additional software.

While harder to configure, it is better solution for quick, reliable restoration onto similar and slightly dissimilar hardware. In a crunch a kickstart install will save you hours of time. It also gives you a perfect opportunity to get the installation and configuration documentation completed.

Keeping both up to date will be another task for the virtualization administrator, but this is also a necessary task in case that disaster happens. The configuration documentation will also help in any reviews of the system for security concerns.

Virtualization expert Edward L. Haletky is the author of "VMWare ESX Server in the Enterprise: Planning and Securing Virtualization Servers," Pearson Education (2008.) He recently left Hewlett-Packard, where he worked in the Virtualization, Linux, and High-Performance Technical Computing teams. Haletky owns AstroArch Consulting, providing virtualization, security, and network consulting and development. Haletky is also a champion and moderator for the VMware discussion forums, providing answers to security and configuration questions.