Running ESXi from Flash Drives for Testing

ESXi allows you to boot from a very small disk requirement. This is the perfect vehicle to use in test virtualization environments to learn more about virtualization or test configurations before you roll them into production. In my private lab, I've decided to boot ESXi from a USB flash device.

For ESXi 3.5, configuring boot from USB flash was a little more work that most people would like to do. There are a number of resources on how to create the USB flash-bootable image, among the most popular being Remon Lam's post at VMinfo.nl.

With ESXi 4, we're now able to do the install from the bootable CD-ROM disk to install upon the USB flash. A few prerequisites need to be configured first, however. The primary requirement is that the USB controller on the server in question is supported as a boot device. This may be configured in the BIOS of the server in question. One of my servers in my private lab is an HP ProLiant ML 350 G5 server. This option is configured in the boot devices section of the BIOS, shown in Figure 1 below:

[Click on image for larger view.]

Figure 1. The server BIOS will permit boot from USB flash functionality.

Different server models may have different boot behavior for USB devices, especially if multiple USB controllers are present. It may be necessary to move the USB flash drive to another interface capable of booting an image. If you want to install ESXi onto a bootable flash from the ESXi product CD, simply ensure that there are no other storage devices accessible during the installation. This includes fibre channel HBAs that may be connected to storage fabric, as well as any local drive arrays or disk on the server.

While this practice is adequate for test and lab use, it's not a production-class configuration. For diskless boot of ESXi, there are two primary options. The first is a dedicated LUN for each ESXi server. This LUN should be masked to only one host. The second is to use a built-in SD Flash to boot ESXi on the server. Newer servers have this option for virtualization-specific configurations. The HP offering (part # 580387-B21) offers a 4GB flash media for the server.

Diskless ESXi boot is nice, especially for lab configurations. Your VMFS volumes, if on local disk, will be preserved in case you need to reload the hypervisor. And thanks to VMFS-3's backward and forward version compatibility, there won't be any surprises down the way.

Are you booting ESXi from flash? What tips and tricks have you learned along the way? Share your comments below.

Posted by Rick Vanover on 12/16/2009 at 12:47 PM