Unix Backup and Recovery

Homegrown Bare-Metal Recovery

There is a better way to restore the current OS configuration to a new disk, without laying down the information twice. This method is simple; here are its steps:

1. Back up all appropriate metadata (disk layout, /etc/vfstab, etc.).

2. Take a good backup of the OS via dump or a similar utility.

3. Boot the system to be recovered into single-user mode using a CD-ROM.

4. Set up the recovery disk to look the same as the old root disk, and mount it.

5. Recover the OS to the mounted disk.

6. Place the boot block on the mounted disk.

7. Reboot.

What Is the Boot Block?

The key to the homegrown bare-metal recovery procedure is the recreation of the boot block. Without it, this procedure doesn’t work. The boot block is the first few blocks of data on the root sector of the disk. (“Boot block” is actually a Sun term, but other platforms have a similar block of boot information.) Each hardware platform knows enough to look here to find the basic “boot” information. The main part of this block is the location on the disk where the kernel is stored. This block of boot information, or boot block, is stored outside, or “in front of, " the root filesystem—on the raw disk itself. Without the boot block, the system will not boot off that disk.

On What Platforms Will This Procedure Work?

I originally developed this procedure for SunOS and Solaris, since Sun did not have a utility like IBM’s mksysb ; however, it is adaptable to many Unix systems. For example, all of the bare-metal recovery chapters ...