Question about two vs. three nodes

[maestro7879]

We currently have 1.9 with 2 nodes connected to a SAN using 10gb fibre.
If we add a 3rd node in 2.0 for HA we will not be able to connect that SAN to the 3rd node because of cost constraints.
Is it possible to not have the 3rd node connected to the storage or should we just use the two node scenario in 2.0 ?

What are the benefits and drawbacks in each scenario ?

 

[e100]

I have essentially the same setup you have but I am using the poor mans SAN, DRBD, on two of my nodes.
The third node is a member of the cluster, but it is not using the DRBD volumes at all.
When I added my DRBD LVM volumes to Proxmox I marked what nodes had access to them.

So far this is working just as I expected.
When testing HA one time I noticed that HA tried to start the HA node on the third no DRBD having node.
It failed, then tried the next node and it worked.

I think it would be nice if we could provide hints to HA that it can only start the VM on specific nodes.
But it looks like, so far, it is at least smart enough to try until it works.

You can use the third node for openvz, you can live migrate those without shared storage

You really should have at least three nodes so you have proper quorum.
For those on a budget I *think*(have not tried) a tiny low powered 64bit Intel Atom CPU would work fine as that third node just to be a quorum member making sure things are working properly.

 

[maestro7879]

I have essentially the same setup you have but I am using the poor mans SAN, DRBD, on two of my nodes.
The third node is a member of the cluster, but it is not using the DRBD volumes at all.
When I added my DRBD LVM volumes to Proxmox I marked what nodes had access to them.

So far this is working just as I expected.
When testing HA one time I noticed that HA tried to start the HA node on the third no DRBD having node.
It failed, then tried the next node and it worked.

I think it would be nice if we could provide hints to HA that it can only start the VM on specific nodes.
But it looks like, so far, it is at least smart enough to try until it works.

You can use the third node for openvz, you can live migrate those without shared storage

You really should have at least three nodes so you have proper quorum.
For those on a budget I *think*(have not tried) a tiny low powered 64bit Intel Atom CPU would work fine as that third node just to be a quorum member making sure things are working properly.

After I made the post I did see the option for allocating the storage to certain nodes. Thanks for confirming this.
I'm going with 3 nodes. The 3rd node will be a server but not as robust as the other 2 main nodes.

 

[dietmar]

I think it would be nice if we could provide hints to HA that it can only start the VM on specific nodes.
But it looks like, so far, it is at least smart enough to try until it works.

Just define and use a 'Failover Domain' - No GUI currently, but should be simple.

 

[e100]

Just define and use a 'Failover Domain' - No GUI currently, but should be simple.

Thanks for the tip!

If others need an example I have bolded the additions to setup a Failover Domain:

  <rm>
    <pvevm autostart="1" vmid="101" [B]domain="vm5-vm6"[/B] />
    [B]<failoverdomains>
      <failoverdomain name="vm5-vm6" restricted="1" ordered="1" nofailback="1">
        <failoverdomainnode name="vm5" priority="1" />
        <failoverdomainnode name="vm6" priority="100" />
      </failoverdomain>
    </failoverdomains>[/B]
  </rm>