IBM Certification Study Guide AIX V4.3 System Support

8.2 The Data Layout of a mksysb Tape

The contents of a mksysb tape are shown in Figure 100.

Figure 100: mksysb Tape Contents

8.2.1 BOS Boot Image

The BOS boot image contains a copy of the system's kernel and device drivers needed to boot from the tape. It is created with the bosboot command. You can also use the bosboot command to remake the boot image on a hard disk.

8.2.2 mkinsttape Image

This image contains the files described in the following sections:

8.2.2.1 ./image.data

This file, created by the mkszfile command, contains information describing the image installed during the BOS installation process. This information includes the sizes, names, maps, and mount points of logical volumes and file systems in the root volume group. It is not recommended to modify this file directly. Changing the value of one field without correctly modifying any related fields can result in a failed installation and a corrupted backup image. The only exception to this recommendation is the SHRINK field, which the user may modify to instruct the BOS installation routines to create the file systems (listed in image.data file) only as large as the actual contents. For example, if a file system is 20 MB with only 4 MB of space actually used by the file system, the SHRINK option will create a file system of only 4 MB in size.

8.2.2.2 ./tapeblksz

This file contains the block size the tape drive was set to when the backup was done. In order to find out what the block size was when the mksysb command was executed, run the following commands:

Rewind the tape using the command:
```
tctl -f /dev/rmtxx rewind
```
Change the block size of the tape to 512-bytes using the command:
```
chdev -l rmtxx -a block_size=512
```
Restore from the second image and extract the ./tapeblksz file using the command:
```
restore -s2 -xqvdf /dev/rmtxx.1 ./tapeblksz
```

8.2.2.3 ./bosinst.data

This file contains the customized BOS install procedures and dictates how the BOS install program will behave. You can customize this file before doing the mksysb.

8.2.3 Dummy TOC

This image is 512 bytes long and contains one file with DUMMY TOC in it. This image is used to make the mksysb tape contain the same number of images as a BOS install tape. If you want to view this file run the following commands:

Rewind the tape using the command:
```
tctl -f /dev/rmtxx rewind
```
Move the tape forward two file markers to stop at the beginning of third file marker using the command:
```
tctl -f /dev/rmtxx.1 fsf 2
```
Restore the third image from the tape using the command:
```
restore -xvdf /dev/rmtxx.1
```

8.2.4 User Data

This image contains all the user data that is to be stored on the tape. The mksysb command uses the image.data file to backup all the files.

8.3 Verifying System Backups