Giving it a remote boot
Boot-from-SAN establishes virtual disks on the SAN and stores the server's boot image, operating system, system settings and applications there. The server boots from the boot image and is connected to the operating system-application-setting image in another virtual disk.
The boot process involves loading the operating system code from the SAN when the server is turned on. The system BIOS is loaded first from a boot image; it initializes the hardware and loads the operating system, checks the hardware setup and creates a copy of the operating system in server memory.
Boot images also can be cloned to accommodate the deployment of multiple servers, each of which has the same identity. For instance, an IT shop may have images on its SAN for Web servers, Microsoft Exchange or SQL servers waiting in queue for deployment. In this way, customers could create physical servers or servers virtualized with VMware or the open source Xen that can be provisioned from the SAN as necessary.
The problem with deploying a boot-from-SAN and LUN-cloning strategy for server provisioning is that it is a manual process that is often complicated to set up.
"With traditional LUN cloning, the user is required to use exactly the same hardware configuration or risk driver mismatches," says William Hurley, senior analyst for the Data Mobility Group.
Walters says Red Hat warned him off boot-from-SAN technology because of all the troubles that could ensue. "It claimed to support boot-from-SAN in no way, and told us all sorts of bad things would happen if we tried," he says.
Each server attaching to the SAN also needs its own boot image. N-Port ID Virtualization from Emulex lets several virtual servers share the same HBA and subsequently the same boot image. Microsoft says it also is working on software to let a non-virtualized blade or other server boot from a single image on the SAN.
Software and hardware from Brocade also make the process of creating and deploying server images easier and more automatic. Brocade's Tapestry ARM, a technology the company acquired last year when it bought Therrion Software, consists of hardware - the Tapestry ARM Appliance - and software - the Tapestry ARM Service Processor. Tapestry ARM integrates into existing Brocade Fibre Channel SAN environments.
"Tapestry ARM uses boot-from-SAN and LUN-cloning technology wrapped up in a server-based software package to make it easier to provision and move and reassign server-to-storage relationships," says Brian Garrett, an analyst with the Enterprise Strategy Group. "Storage arrays that support boot-from-SAN and LUN cloning are missing the server-based software, that is, the boot manager."
ARM provides the missing automated boot-from-SAN and server-provisioning piece. "In ARM, more than one host computer can boot from the image," Hurley says. "Traditional [preexecution] boot is normally a one-to-one operation," he adds.
With ARM, each server boots to the same image, and the Tapestry ARM Service Processor software picks up the individual applications, operating systems and configuration settings for the server from images stored on the SAN. When a new server needs to be deployed, Tapestry ARM communicates with the Fibre Channel HBA in the server and tells it where to find its operating system and application data on the SAN. The ARM software automatically accommodates differences in server hardware, letting a server with a different hardware configuration be swapped in if a server fails.
"If a server fails, [ARM] can direct another server to the first server's LUNs," says Randy Kerns, an independent storage analyst.
The ARM system keeps a repository of images for each type of server. These images may be called on and configured from the Tapestry ARM management interface. Tapestry ARM uses Microsoft's VHD technology, which captures the operating system and applications for the virtual machine in a single file. Among those vendors licensing VHD are BMC Software, Fujitsu-Siemens, Network Appliance, Softricity, Virtual Iron, XenSource and Brocade, which includes it in Tapestry ARM.
But the real advantage of Tapestry ARM is that it automates server deployment and provisioning. Whereas boot-from-SAN and LUN cloning are manual processes, Tapestry ARM's management interface can automatically carve out virtual disks and assign servers to LUNs.
Matthew Deveny, architecture manager for Sutter Health in Sacramento, Calif., has beta tested Brocade's Tapestry ARM. "We are front-ending an application out to 41,000 employees. Deploying, managing and provisioning that environment can be extremely complicated for those machines. We believe it can save us a lot in overhead in provisioning resources and ultimately allow us to take drives out of our blade and other servers," he says.
Walters of the Public Broadcasting Service agrees. He says, "The time is finally right for boot-from-SAN."