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Understanding System Image Utility (SIU)

System Image Utility (SIU) is an application that you can use to create Mac OS X v10.6 network disk images. SIU is located in the /Applications/Server folder on your Mac OS X Server v10.6 computer, or it can be installed as part of the Server Admin Tools v10.6 on any Mac OS X v10.6 computer. Network disk images are modified system images that have been created for use with the NetBoot service. As you can probably tell from the name, NetBoot allows you to start multiple Mac computers via a network connection to network disk images hosted on a Mac OS X server. NetBoot is Apple’s primary network-based system deployment mechanism, and as such, is one of the primary topics of Chapter 5, “Deploying System Images.”

Though SIU is primarily designed to facilitate the NetBoot service, it’s introduced in this chapter because it’s the only Apple tool that provides an easy-to-use automated method for creating deployable system images. Specifically, SIU in Mac OS X v10.6 introduces a new network disk image type, NetRestore, which can be used to create and deploy system images. Further, even if you don’t intend to use the Mac OS X NetBoot service, you can still use SIU as an automated tool for creating full system images to be deployed using another mechanism.

Selecting a Network Disk Image Source

Although Mac OS X Server v10.6 supports hosting images with previous versions of Mac OS, the 10.6 version of SIU can only create network disk images of Mac OS X v10.6.x or Mac OS X Server v10.6.x. Therefore, if you wish to create network disk images of previous versions of Mac OS X you must also use previous versions of the Mac OS X Server administration tools.

As when creating a standard system image, you must have a source from which to create your network disk images. SIU can create network disk images of Mac OS X or Mac OS X Server from two primary sources; Mac OS X installation media or any system volume that is not currently booted. Additionally, SIU treats the contents of a mounted disk image identically to that of a standard volume. Thus, if a disk image volume’s contents constitute a copy of the Mac OS X installation media, SIU will recognize the mounted volume as installation media. Conversely, if a disk image volume’s contents are that of an installed and configured system, SIU will recognize the mounted volume as a nonbooted system volume.

Network Disk Image Types

System Image Utility creates three types of network disk images:

  • A standard NetBoot image provides a typical computing experience, albeit one that is hosted from a NetBoot server. When started from a NetBoot image the Mac operates nearly identically to a locally booted Mac OS X client or server. Although this is an ideal configuration for systems that will remain running from the NetBoot image, it is not generally used for system deployment purposes. This is because most Mac computers come with ample local hard drive space, and more often than not, are portable computers. Thus, relying on a permanent network connection for the system volume generally isn’t the best use of resources.
  • A NetInstall image starts up to the Mac OS X Installer, much like when you start up from the Mac OS X installation media. In essence, you’re simply taking the original Mac OS X installation media and making it available on the network. Thus, NetInstall allows you to perform an installation of the operating system to a local Mac. This is an alternative to pure system imaging techniques that restore a premade system image to the local Mac. The advantage to NetInstall is that you can pick and choose the individual packages that get installed, as opposed to performing a system restore, which always includes the entire contents of the system image.
  • New to Mac OS X v10.6, a NetRestore image starts up to an interface that appears to be identical to the Mac OS X Installer. However, instead of performing an install of Mac OS X, it will restore a system image to the local Mac. The restored system image is based on either a clone of your model system or a modular system built by SIU. This is the deployment mechanism of choice for many because it provides the fastest method for deploying a fully configured system.

SIU Network Disk Image Results

SIU features a two-mode interface that allows you to create either basic network disk images with just a few clicks or more complicated images based on a customized workflow. This chapter focuses on the “basic” mode while Chapter 5, “Deploying System Images,” focuses on building customized network disk images with SIU.

When using the “basic” SIU mode, there are two main choices you make; selecting the Mac OS X system source and choosing the network disk image type. The resulting image created by SIU will vary based on the selected source and type of image you are creating.

If your system source is Mac OS X installation media, and you choose to create a...

  • NetBoot image—A Mac booting from this image will start up to a fully functional, though completely generic, version of Mac OS X based on the installation media. This is not a very useful build combination when using SIU in “basic” mode.

  • NetInstall image—A Mac booting from this image will start up to an installer interface identical to that based on the installation media. This allows you to provide access to the installation media from the network.

  • NetRestore image—A Mac booting from this image will start up to an interface allowing you to restore a generic system image based on the installation media. In other words, SIU will build a restorable system image by installing Mac OS X to a disk image based on the default installation settings. Again, when using SIU in “basic” mode this is not a very useful build combination. However, this combination provides the basis for building a modular system image, as covered later in this chapter.

If your system source is a nonbooted system volume, and you choose to create a...

  • NetBoot image—A Mac booting from this image will start up to a system identical to that of the source system volume. This allows you to provide access to a fully configured system from the network. This combination is used most often for “diskless” deployments wherein the local Mac does not have a system installed; it instead relies solely on a NetBoot system. This combination is also used to create an administration, maintenance, and recovery system that can be accessed from the network.

  • NetInstall image—SIU will not let you select this combination because the source is not valid Mac OS X installation media.

  • NetRestore image—A Mac booting from this image will start up to an interface allowing you to restore a system image based on the source system volume. In other words, SIU will build a restorable system image by cloning the source system. While you could certainly do this yourself using the manual methods outlined previously in this chapter, SIU takes this to the next step by “wrapping” the restore system image in a NetRestore system. The image built by this combination, when hosted from a NetBoot server, is the easiest method to deploy a cloned system image via the network.

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