How should I use LVM with Ganeti?
- by javano
I am building a small Ganeti cluster on some low end hardware (I only have the resources given sadly). I am confused as to the use of LVMs with DRBD. I have two instances and three nodes.
What I want is instance1 replicated between node 1 & 2, and instance2 replicated between nodes 3 & 2 (so node2 is doing nothing, except waiting for either node1 or 3 to fail, is it is the secondary node for both instances). This is because node2 is a lower hardware spec than 1 and 3, so I just want it as an hot-spare.
How can I achieve this? I don't want instance1 being replicated to node3 for example, nor instance2 replicated to node1.
Nodes 1 & 2 have /dev/sda5 which is 150GBs (for example).
Nodes 2 & 3 have /dev/sda6 which is also 75GBs (for example).
Using just nodes 1 & 2, after looking at the Ganeti docs I would;
vgcreate my-vg
Next I would create the cluster via gnt-cluster VG = "my-vg".
It is here I believe that I am missing some knowledge. I believe that what I need to do is create the same Logical Volume on nodes 1 & 2 in Volume Group "my-vg", that solely consists of /dev/sda5 and call it "lv1". Then create an Logical Volume on nodes 2 & 3 the solely consists of /dev/sda6 in "my-vg" that is called "lv2".
When creating instance1 I would then use "-vg=lv1 -n node1:node2", and when creating instance2 I would use "-vg=lv2 -n node3:node2".
I breifly had a go at this today and I'm dubious if this will be possible. When trying to create instance2, "lv2" wont exist on node1 (the cluster master) so I don't believe it will allow the instance creation.
Could I create a 1kb parition (/dev/sda6) on node1 and put it into a LV called "lv2" or is that too flakey? Is this set up possible?
Thank you.
