Best setup for Main server + backup server which is not 24/7

[Thomas Stone]

Hello:

For the past year or two I have run a 'main' Proxmox server which runs a few VMs but also handles NAS duties. Then I have a 'backup' Proxmox server which boots up for an hour a day and does backups using pve-zsync. All storage is local.

The problem is I created the pair as a cluster, and this creates problems of course with quorum, if the backup server is off then for example a power-failure reboot (or even a VM reboot) fails because of no quorum. I have gotten used to typing pvecm expected 1 frequently!

I am one major version behind, so I'm ready to update and wondered with the latest features how you recommend I set things up. Unless there are new options to solve the lack of quorum problem, it seems I should NOT create a cluster next time.

Thanks!

 

[wolfgang]

Hi,

Unless there are new options to solve the lack of quorum problem, it seems I should NOT create a cluster next time.

This is not a problem this is design.
With 2 nodes you never can know what state the cluster has.

Expect this 2 nodes only the cluster network get lost.
So every node is thinking the other node is down but this is not true.

Here you can read the hole story ;-)
https://en.wikipedia.org/wiki/Byzantine_fault_tolerance

 

[Thomas Stone]

Yes, I meant only that in my case of only two nodes (master and sporadically-online backup) the normal cluster function does not work for me.

My question was, now that I have read further and know the name of the service, can I use Storage Replication (pvesr) to keep a daily-updated backup on my second machine WITHOUT creating a cluster which causes me the problems?

My reading of the page ( https://pve.proxmox.com/wiki/Storage_Replication ) indicates that the new pvesr DOES require a cluster, so is not useful in my use case. Is that correct? My option then is only to have two independent Proxmox machines and use pve-zsync? Thank you.

 

[wolfgang]

(master and sporadically-online backup)

I'm not clear with this sentence?
Does this mean you start the backup node and than sync the data and after the job is done the backup node will shutdown?

 

[Thomas Stone]

Yes, exactly.

 

[wolfgang]

In this case, but only in this you can give the productive node a vote of 2.

This would give you quorum without the backup node.

If the first node is down the backup node must be activate with expected 1.

With this setup you can use a cluster and pvesr.

 

[Thomas Stone]

In this case, but only in this you can give the productive node a vote of 2.

This would give you quorum without the backup node.

Oh, that sounds great. How do I give that machine a vote of 2? Thanks!

 

[Thomas Stone]

maybe ...

on 24/7 'master':

/etc/pve/corosync.conf

quorum_votes: 2

anywhere else?

 

[wolfgang]

You can set them when you crate the cluster.
see

pvecm help

 

[Thomas Stone]

ah... should I assume the fact that not even root can write this file means it is impossible to change it after cluster creation, or can I be cheeky and change it anyway?

-r--r----- 1 root www-data  434 Sep 25  2016 corosync.conf

 

[wolfgang]

If you have already a cluster you can set it direct in the corosync.config.
But edit /etc/pve/corosync.conf.
To apply this config you have to restart the corrosync service.

 

[Thomas Stone]

#man pvecm helped me out! In case it helps anyone else:

#pvecm create clustername --votes 2

will create a new cluster (as long as none exists) and give 2 votes (instead of normal 1) to the machine on which you created the cluster, the first node.

Probably most people should not do this, but I think it is a good option for my purposes.