This article was taken from the entire eighth chapter of the Sun BluePrints book, JumpStart Technology: Effective Use in the Solaris Operating Environment by John S. Howard and Alex Noordergraaf (ISBN 0-13-062154-4.).
WebStart Flash provides a mechanism by which a specific or reference installation of the Solaris OE is archived. That archive can then be used to install the Solaris OE. The reference installation is created from the on-disk Solaris OE, which includes all installed software. This system is designated as the master machine. The reference installation can be a Solaris OE installed by any means, for example, with JumpStart software, from CD, or by an interactive installation.
After the master machine is identified, the reference installation is captured in a Flash archive. A central feature of Flash, this archive is essentially a point-in-time snapshot of the Solaris OE, software patches, and applications on the master machine.
The Flash extensions enable administrators to install the archive from an NFS server or an HTTP server, in addition to installing from a traditional JumpStart server. Additionally, the archive can be accessed from a disk device (including CD-ROM) or tape device local to the installation client. The Flash archive is transmitted over the network to the installation client and written to the disk. After the archive is written to the installation client's disk, any necessary archive modifications are performed. For example, configuration files, such as /etc/nsswitch.conf, on the installation client may need to vary from the file on the master machine. The Flash mechanism enables automation of modifications and allows for differences in kernel architecture or device differences between the master machine and the installation client.
Additionally, Flash enables automatic resolution of partitioning differences between the master machine and the installation client. For example, if the Flash archive was created on a system with a single root (/) partition and the installation client has separate / and /var partitions, the Flash archive automatically customizes itself to the installation client. Remember, the installation client partitioning must be correctly specified in the JumpStart software profile.
The Flash archive is a snapshot of a system and, as such, includes all specified files on that system. If a Flash archive is created from a system in use, some files need to be cleaned up or zeroed out after the Flash archive is installed. Examples of these types of files include log files, such as those found in /var/adm and any files in the /var/tmp directory. Log files can be easily zeroed out from a finish script after installation. In the case of temporary directories, such as the /var/tmp directory, it is recommended that they be excluded when the Flash archive is created.
The Flash archive should be created after all software has been installed but before the system has gone into production. And, depending on the software installed and the intended use for the system, the Flash archive may need to be created after the software is installed but before the software has been configured. For example, a database server or LDAP server should have its archive created after the database management software has been installed but before the databases have been created and populated.
An initial installation must be done when a Flash installation is performed. Flash cannot be used to upgrade a system.
Installation of the Solaris OE with a Flash archive can be dramatically faster than with other mechanisms, depending on factors such as network traffic and disk speeds.