mksysb backups make AIX recovery easy
If you ever need to restore your AIX system, you'll need a reliable OS backup. You can create this via the mksysb command, which, as the name implies, makes a system backup. That's not to say it gets your entire AIX system, but it does create a backup of the OS itself, the root volume group. For any other volume groups you'll need to rely on other backup utilities.
You might need to build a system from a mksysb for disaster recovery or if your OS has become corrupted, but those aren’t the only times a backup comes in handy. A mksysb is a simple and effective way of migrating to new hardware. It can also be used to clone an existing AIX system. For example, you could create a Standard Operating Environment (SOE) LPAR, take a mksysb backup of it and use that to build new LPARs.
Tracing Your Roots
A mksysb is much more than a backup of the files in the rootvg file systems. It includes a boot image, optional software that has been installed into rootvg and system informational files. The mksysb contains the layout of the rootvg logical volumes and the file systems. This is important, as those file systems get created as part of the mksysb restoration process. That saves a lot of work and time. Restoring a mksysb even gives you the option of recovering your devices, so you don't have to reconfigure network settings, disk attributes and so on. You'd normally use this only when you're restoring onto the same system you backed up.
In the days of stand-alone systems, the mksysb command would write to a dedicated device such as a tape drive. Today it's more common for the mksysb to be written to a file on disk and stored on a different LPAR. That way it can be made ready for use without needing to load physical media such as tapes or DVDs.
At Your Command
The mksysb command can be run from the command line or using the SMIT fastpath smitty backsys. You have to specify the output device or file. The mksysb file that’s created is typically between 2 and 4 GB, but it could be much larger, depending on the size of your rootvg. The target file system needs to have enough space for this file, and be large-file-enabled. The ulimit should be set to unlimited for the user who runs the backup.