This post shows how to set a multi-node Disk Heartbeat –
smitty cl_manage_mndhb. What is the difference between the traditional and the multi-node disk heartbeat? The first one is a “network” between two nodes where one disk is shared between only two nodes. The second one allows one disk to be shared by multiple nodes. The second one requires creation of a logical volume. The first one does not need any volumes. The principle of the “single point of failure” still applies – it is not a good idea to have only one mult-inode heartbeat disk in a cluster.
Executing this shortcut, administrator is presented with a screen allowing the following choices:
Create a new Volume Group and Logical Volume for Multi-Node Disk Heartbeat Add a Concurrent Logical Volume for Multi-Node Disk Heartbeat Show Volume Groups in use for Multi-Node Disk Heartbeat Stop using a Volume Group for Multi-Node Disk Heartbeat Configure failure action for Multi-Node Disk Heartbeat Volume Groups
It is peculiar that the first two options imply creation of a logical volume…. after creating these entities using the standard method does not require me/you to create a logical volume.
I tried this option today, and I have to say that I really like it as it is a simpler one which does all in a single step. But I failed the very first time I did it. Looking at the ouput form
smitty it very quickly became apparent why. See for yourself – the error message:
Error executing mklv -y mndhb_lv_01 -u 1 -c 1 -e m -t jfs -v n -w n -r n mndhb_vg_01 32 hdisk2 on node #####
The last line shows a request to create a logical volume which size equal 1 x 32 = 32MB. What size is the disk (
hdisk2) I specified for this action?
bootinfo -s hdisk2 20
This disk is 20MB. How it is possible to fit a 32MB logical volume in a 20MB physical disk? It is not possible!!! So for me to get this show running, I had to ask SAN administrator to “expand” this and the LUN from another SAN controller (another fabric) to 40MB (I like this “round” number). Next after
chvg -g vg_name to make AIX aware of the new disk size, I could finish what I intended to do.
From now, I have to remember to always ask for 40MB LUNs if they are intended to be used as the “multi-node” heartbeat disks.