AIX Bootlist Considerations

When you have multiple paths to a boot LUN on a Oracle FS System, the Oracle FS Path Manager (FSPM) ensures that the system uses an alternative path to the LUN if one fails while AIX is running. However, FSPM is not involved when the system starts booting.

The system firmware uses a list of paths to boot devices known as the bootlist. It tries each entry in the bootlist in turn until it is able to boot the system from one of the devices. If you wish to be able to boot from a multipathed LUN when some paths have failed, you must make sure that multiple paths to the LUN appear in the bootlist.

The bootlist is set up in AIX using the bootlist command. For example, the following command requests AIX to set the bootlist up so that the system attempts to boot from hdisk3, but if it fails to do so it should try hdisk5.

bootlist -m normal -o hdisk3 hdisk5

There are two important points to note when setting the bootlist with multipathed devices:

If the disk names you pass to the bootlist command are for multipathed disks, the command converts each disk name into a list of all paths to that disk which are in the available state at the time.
In the example above, if there are eight available paths to hdisk3 the command attempts to create a bootlist consisting of the eight paths to hdisk3 followed by however many paths there are to hdisk5. It is not possible to control the order of individual paths to a multipathed disk.
Only a limited number of entries are allowed in the bootlist.
The number allowed depends on the hardware model of your system. Some systems allow five entries, for example. In the example above where there are eight available paths to hdisk3 and the system allows five entries in the bootlist, the command would set up a bootlist containing five paths to hdisk3 (chosen effectively at random out of the eight available) and no paths to hdisk5.

After you install FSPM on a system booted from a Oracle FS System LUN.

Oracle recommends that you use the bootlist command to set the bootlist appropriately for your situation. Although you cannot control the order in which individual paths to a LUN will be placed in the list, you can control how many paths get added, and which ones. The bootlist command only adds paths that are in the available state. You could use the rmpath command to temporarily make some paths unavailable while setting up the bootlist. Alternatively, you could use port masking on the Oracle FS System, or configuration utilities on your SAN switches, to temporarily remove paths from the configuration, then reboot the host to take the paths out of the available state.