Want to use AIX live update but can't because you're running low on free/spare CPU capacity on your Power Systems frame?
Well, with the latest TL for AIX 7.2, you now have a couple of options to help mitigate this problem. On a busy frame, it might be difficult to keep enough free CPUs to allow the creation of the surrogate partition or to run several Live Updates concurrently. Now you can try one of the following solutions:
I was particularly interested in the "Live Update CPU Reduction" approach. I performed a couple of tests and found that, in order to use this particular feature, I needed to add the "cpu_reduction = yes" stanza to the /var/adm/ras/liveupdate/lvupdate.data config file. The documentation states that this new option will do the following:
# cpu_reduction = <yes | no> Blank or omitted defaults to no. If yes, the
# live update operation will, in the absence of sufficient processing
# capacity to create and boot the surrogate normally, determine whether
# removing some capacity from the original would result in sufficient
# available capacity, and if so, will automatically remove
# the capacity from the original (later to restore the surrogate to full
# capacity once the original is deleted).
root@lkutest / # oslevel -s
root@lkutest /var/adm/ras/liveupdate # cat lvupdate.data
cpu_reduction = yes
WARNING! The "white space" in front of the "cpu_reduction = yes" line MUST exist (see below). I added a tab. Without this, the option is NOT recognised by the live update (geninstall) command. This is not documented anywhere and I'm hoping it will not be a requirement in a future AIX update.
You can verify the option has been recognised by performing a preview and then checking the liveupdate.cf afterwards. It should show CPU_Reduc set to yes.
root@lkutest /var/adm/ras/liveupdate # grep -p CPU liveupdate.cf
do = "yes"
You can find more information on the "cpu_reduction" option here: https://www.ibm.com/support/knowledgecenter/ssw_aix_72/com.ibm.aix.install/lvupdate_configuration.htm
With the CPU reduction option, during a live update operation (geninstall -k), the surrogate VMs entitled capacity is "shrunk" to the minimum allowed in the partition profile. After the operation is completed the VM is "resized" to match the original capacity entitlements. This all happens automatically. The following screens shots, from PowerVC, show the VMs "Processing units" before, during and after the live update. They also show the resource alocation and resize operations from the PowerVM Messages view. You can see that the assigned "Processing units" were reduced to 0.1 (based on the VMs partition profile minimum CPU setting; check with 'lparstat -i | grep Mini | grep Cap' on the AIX VM).
If you don’t use this option and your frame doesn’t have enough CPU capacity to house the surrogate partition, the live update preview will fail, with the following message.
1430-200 FAILED: Not enough processing units available on target host.
Here's a brief overview of these new options with Live Update.
Live update with CPU (processor) reduction:
Live Update Across Frames: