Restoring the Operating System

You can use one of two methods for recovering the operating system during a disaster recovery: complete or partial. When you perform a complete reinstallation, you install all operating system files and recreate any unique configurations that existed before you lost data or experienced a disk crash. To perform a partial reinstallation, install the minimum number of files and make the minimum number of configurations necessary for creating a fully operational networked system. Then, later, recover the remaining operating system and configuration files using Backup.

Figure 1-5 illustrates the steps for recovering from a disk crash where you lost the operating system, Backup software, and server indexes and configuration files. It also outlines the two choices you have for reinstalling the operating system.

Figure 1-5 Recovering From a Disk Crash With Operating System Loss

Performing a disaster recovery for Backup servers and clients is very similar, except on client systems you do not need to recover the server indexes and configuration files.

Complete Installation

In some cases, it might be faster to perform a complete reinstallation of the operating system, especially if you install the operating system from a CD and have very few special configurations to recreate. Depending on the speed of your backup device and network, it could potentially take longer to recover the remainder of your files and configurations using Backup during the disaster recovery procedure.

If you use a device with a default configuration that is not directly supported by the operating system, you also need to modify the device configuration files during installation:

• You might need to modify the /kernel/drv/st.conf file to support a DLT tape drive.

• For SunOS systems, modify the /usr/sys/scsi/targets/st_conf.legato.h file.

When you recover the remainder of your data, you can decide whether you want to replace the operating system files you just reinstalled with the operating system files backed up by Backup. If you want to guarantee that you have the same configurations prior to the disaster, replace the files and configurations you created during the installation.

Partial Installation

On the other hand, a partial installation might get your Backup server up and running more quickly, so you can concentrate on continuing the disaster recovery. Later, you can recover the remainder of your operating system files using Backup. You will especially save time if you have a large number of clients and devices on the network that need to be configured; it will take you time to find IP addresses, hostnames, and recreate configurations.

Furthermore, if you wait to recover the remainder of the operating system files with Backup, you will be assured that the server, clients, and devices will be reconfigured exactly as they were prior to the disaster.

If you choose to do a partial install, you need to perform the following tasks:

• If necessary, select a domain for the system.

• Install the basic operating system files and device driver software.

• Make sure the system communicates properly over the network.

After you reinstall the operating system, whether you did a complete or partial installation, run the tar command to verify that the tape drive is functioning properly.