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How Xsigo Makes It Easy to Realize the Benefits of VMware ESX SAN Boot

The Advantages of SAN Boot
Remote boot is becoming increasingly common in state-of-the-art data centers where flexible and
efficient use of resources is an important goal. SAN boot is a technique for booting servers from a
boot image which is stored on a target WWPN and LUN within the SAN, rather than an image on a
local disk.


Date: 10 Jan 2011



Booting VMware ESX from a SAN includes the following benefits:
??? Enables diskless servers and blades. Servers can be denser, more reliable, and run cooler
without internal storage.
??? Enables the seamless replacement of one physical server with another. The identity of a
physical server is determined by its boot image and its I/O connectivity. The Xsigo I/O
Director makes it possible to assign both the boot image and the I/O identity in a dynamic
fashion, so physical servers are interchangeable.
??? Enables server repurposing. Servers may be repurposed easily between running ESX and
running other hypervisors or native operating systems such as Linux or Windows.
??? Improves image management. Boot images can be created and managed more easily when
stored on the SAN rather than scattered across the local disk drives of servers. This is
particularly true for data centers with a large number of servers.
??? Enables easier image backup. Boot image backup can be included in the standard SAN
backup process. There is no need for a special backup technique for backing up and
restoring images stored on local disk drives.

How the Xsigo I/O Director Helps
The Xsigo I/O Director is an I/O virtualization system which provides flexible virtual NIC (vNIC) and
virtual HBA (vHBA) resources and connectivity to servers instead of the fixed resources and
connectivity of traditional physical NICs and HBAs (Figure 1). vNICs and vHBAs are configured on
the I/O Director for each server. These virtual I/O adapters can be used just like physical I/O
adapters on the servers. The MAC addresses of vNICs and the WWNs of vHBAs are exposed on the
LAN and SAN just like those of physical I/O adapters. The Ethernet and Fibre Channel termination
ports of the vNICs and vHBAs can be set by the administrator.

I/O profiles with vNICs and vHBAs are assigned to the servers, and these I/O profiles can be
changed dynamically or even migrated between servers. Hence, the I/O identity of a server may be
changed, and one server may assume the I/O identity of another server.

Xsigo I/O Director vHBA SAN Boot Capability
The I/O profile of a server may contain the target WWPN and LUN information of its boot image. The
I/O Director makes it possible to boot a server from the SAN over a vHBA using the configured
target information. The configuration is performed on the I/O Director through the Xsigo
Management System (XMS).

Ease of SAN boot configuration is one of the strengths of the Xsigo solution. It is possible to perform
the SAN boot configuration for all servers from one place – the XMS GUI. Targets and LUNs are
automatically discovered, and a wizard is provided to make configuration as easy as possible.
Figure 2 shows one of the screens of this wizard, where the user selects the WWPN of the desired
boot target. The configuration can be performed using CLI commands as well.

This method of SAN boot configuration simplifies the task considerably. The typical method when
using traditional HBAs is to configure boot targets using the BIOS settings of the HBA of each
individual server. This is unwieldy, error-prone, and hard to perform in a large data center. SAN boot
management becomes much more tractable with the Xsigo solution, and dynamic changes to the
boot image for server repurposing become feasible as well.

As noted, ESX SAN boot has many advantages when compared to local boot, including easier
management of images on the SAN, and easier server repurposing. However, SAN boot
configuration, image installation, and image management for a large data center can still be
challenging. One aspect of this is configuring the HBAs on the servers to boot from SAN, and
configuring them with the target information. This cumbersome task is completely eliminated by the
I/O Director as explained above, and it is replaced with easy configuration from a central
management system. The Xsigo solution provides additional tools that make the task of ESX SAN
boot management easier for large data centers, as we will now discuss.

Consider the task of providing ESX SAN boot in a data center with a significant number of servers.
This is illustrated in Figure 3 where 120 servers are connected redundantly to two I/O Directors. The
I/O Directors are connected to the LAN and the SAN. The task is to install 120 ESX images to LUNs
on the SAN, and to configure the I/O Directors to boot the servers from the appropriate images. The
ESX images will be almost identical for all the servers, so installing 120 images from scratch would
be inefficient. We would like to start with a single image, and then replicate it with some minor
customization for all the servers. Note that the differences between the servers are in the guest
operating systems that they run on top of ESX, and in the applications that they run within the guest
operating systems. The ESX image itself will be almost identical for all the servers.

An outline of the process for achieving this task is as follows:
1. Configure a vHBA with access to the SAN for all the servers through the Xsigo
Management System (XMS).
2. Create the master ESX boot image from which all other images will be generated. This can
be done by installing ESX in the standard way to a local disk, and then copying the resulting
image to a LUN.
3. Copy the created image to a LUN on the SAN which will contain the first SAN boot image.
Xsigo provides a script for performing this copy.
4. Duplicate the image to additional LUNs on the SAN so that each server has a boot LUN
with a boot image. Xsigo provides a script for performing this duplication.
5. Customize the boot images. A few customizations of the images need to be performed,
such as updating the UUID data. Xsigo provides a script for performing these
6. Use XMS to enable SAN boot for the servers, and point each server to the target WWPN
and LUN where its boot image is located.
With this simple and efficient process the administrator can easily create ESX boot images for a
large number of servers, and have the servers booted up from their SAN images. This shortens
considerably the time from a decision to provision the servers for ESX to the time when the servers
can be up and running.

New data centers are architected to provide increased efficiency and flexibility as well as easier
management. Server virtualization is one of the key elements of this trend. The Xsigo I/O Director
complements server virtualization by replacing fixed and inflexible I/O resources with dynamic and
scalable resources. A truly virtualized data center is not possible with fixed physical server I/O
ESX boot from SAN enhances data center architecture. Among its benefits are: support for diskless
servers and blades, seamless replacement of one physical server with another running the same
exact image, and easier image installation, management, and backup. The Xsigo I/O Director
provides a complete ESX boot from SAN solution with centralized management using a GUI or CLI,
and scripts for image duplication and customization. With the I/O Director, the task of building an
ESX SAN boot solution for a data center of significant size is much more tractable and
straightforward than with traditional I/O solutions.

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