Question
This technote discusses an enhancement to AIX to allow setting specific paths to boot from.
Answer
In AIX 6.1 TL 6 (6100-06-00) a new feature was added to allow a system administrator to specify which paths would be used to boot from in a multipath environment. This was added by APAR IZ72620 (PTF U838753). The feature was also added to AIX 7.
BOOTLIST OUTPUT
The bootlist will now print the path ID of each path on output:
# bootlist -om normal
hdisk0 blv=hd5 pathid=0
hdisk0 blv=hd5 pathid=1
In this example there are two paths to the boot disk.
SETTING THE BOOTLIST
To set the bootlist to specific paths, list each path on the command line:
# bootlist -m normal hdisk0 blv=hd5 pathid=0 pathid=1
or
# bootlist -m normal hdisk0 blv=hd5 pathid=0,1
Using this method paths can be ignored or deleted from the boot list. This may be necessary if there are more than 5 paths to a boot device, as the Open Firmware for pSeries systems only allows 5 devices (or paths) maximum in the boot list. For example if there are 8 paths to a boot disk, there is a 3 out of 8 chance that the multipath device driver will pick a path not in the boot list. If that happens the boot will most likely hang with an LED 554 "UNKNOWN BOOTDISK" error.
Path ordering is also maintained in the bootlist. If a user wishes to have paths 2, then 1, then 0 searched or booted from, using "pathid=2,1,0" will follow this ordering during the boot.
LIMITING COMMANDS TO A SINGLE PATH ID
Additionally, pathing commands such as rmpath, mkpath, lspath, etc have been enhanced to add the "-i" flag. This flag will limit the command to only use that path ID.
# lspath -i 0
Enabled hdisk0 fscsi0
Enabled hdisk1 fscsi0
DISPLAYING A PATH ID
The "-t" argument has also been added to the lspath command to allow the user to see the path IDs.
# lspath -t
Enabled hdisk0 fscsi0 0
Enabled hdisk0 fscsi1 1
Enabled hdisk1 fscsi0 0
Enabled hdisk1 fscsi1 1
or, to list out all the paths to a specific disk:
# lspath -t -l hdisk0
Enabled hdisk0 fscsi0 0
Enabled hdisk0 fscsi1 1
The path ID is the last digit of the output.
The bootlist will now print the path ID of each path on output:
# bootlist -om normal
hdisk0 blv=hd5 pathid=0
hdisk0 blv=hd5 pathid=1
In this example there are two paths to the boot disk.
SETTING THE BOOTLIST
To set the bootlist to specific paths, list each path on the command line:
# bootlist -m normal hdisk0 blv=hd5 pathid=0 pathid=1
or
# bootlist -m normal hdisk0 blv=hd5 pathid=0,1
Using this method paths can be ignored or deleted from the boot list. This may be necessary if there are more than 5 paths to a boot device, as the Open Firmware for pSeries systems only allows 5 devices (or paths) maximum in the boot list. For example if there are 8 paths to a boot disk, there is a 3 out of 8 chance that the multipath device driver will pick a path not in the boot list. If that happens the boot will most likely hang with an LED 554 "UNKNOWN BOOTDISK" error.
Path ordering is also maintained in the bootlist. If a user wishes to have paths 2, then 1, then 0 searched or booted from, using "pathid=2,1,0" will follow this ordering during the boot.
LIMITING COMMANDS TO A SINGLE PATH ID
Additionally, pathing commands such as rmpath, mkpath, lspath, etc have been enhanced to add the "-i" flag. This flag will limit the command to only use that path ID.
# lspath -i 0
Enabled hdisk0 fscsi0
Enabled hdisk1 fscsi0
DISPLAYING A PATH ID
The "-t" argument has also been added to the lspath command to allow the user to see the path IDs.
# lspath -t
Enabled hdisk0 fscsi0 0
Enabled hdisk0 fscsi1 1
Enabled hdisk1 fscsi0 0
Enabled hdisk1 fscsi1 1
or, to list out all the paths to a specific disk:
# lspath -t -l hdisk0
Enabled hdisk0 fscsi0 0
Enabled hdisk0 fscsi1 1
The path ID is the last digit of the output.
