iSCSI do or dont for HA Cluster

[Mark van de Louw]

Small index of our current cluster:
3 Hosts, local ZFS storage only. Hourly backup to 2nd location.

This night we got a call from our main customer that his VM was not responsive, after a trip to the DC i've discovered that the network card was dead. As it happened in the night with no activity, there is (luckely) no data loss, and we were back up in running in a few minutes.

Today i purchased a SAN. But here comes the question:

The rep at our DC told me this afternoon that an iSCSI LUN can only be accessed by a single host at a time, to prevent Corruption/dataloss.

Is there a way to share a single iSCSI volume across the cluster, so we can enable the HA function of Proxmox? Or is it an better idea to return the SAN tomorrow when it comes in?

Kind regards!

 

[dietmar]

Is there a way to share a single iSCSI volume across the cluster, so we can enable the HA function of Proxmox?

Proxmox VE has integrated cluster wide locking to make sure it is only accessed by a single host.

 

[Mark van de Louw]

Thanks for the fast response!

If Proxmox locks a volume, how can the volume be shared with all the other hosts so we have a working HA setup?
the setup will be: 2 datastores, one on 15K drives and the other with only SSD's. On those 2 stores we will place all VM's of the cluster.

 

[alexskysilk]

The rep at our DC told me this afternoon that an iSCSI LUN can only be accessed by a single host at a time, to prevent Corruption/dataloss.

This is unacceptable for cluster use. As you can imagine, for failover or live migration, the other host has to have access to the volume. Make sure the LUN is accessible by all cluster members for read/write access; as Deitmar stated, Proxmox will handle contention.

 

[Mark van de Louw]

Can you maybe tell me how it works with VMs on multiple hosts, stored in the same volume?

is it smarter to create a seperate volume for each host, or will it function with multiple hosts on one volume?

 

[alexskysilk]

Sure.

Whats important to understand is the difference between volume group and logical volume. When you set up the volume manager on the LUN (either LVM or ZFS) the first layer on the disk is the volume group. each virtual machine creates its own logical volume(s) in the volume group, which are in turn mapped as block devices to the virtual machine. Proxmox will do this part for you- your responsibility would be to provision the LUN and create the volume group.

When the virtual machine is moved to another node, it simply refers to the same logical volume(s) on the same volume group, which is live and accessible by the host node; for this to work the LUN must be accessible to the target node as well as the source node.

 

[Mark van de Louw]

Hello Alex,

Thanks for your extensive explanation! It finaly makes me understand how the connection between the iSCSI part and the cluster should work. I will configure the setup as described, thanks again!

 

[dietmar]

Can you maybe tell me how it works with VMs on multiple hosts, stored in the same volume?

Proxmox can create an LVM VG on to of your iSCSI volume ...

 

[myeter]

Hello,
I created cluster-ha with iscsi on proxmox 6.x (debian 10)
I shared my post bellow, I am late for this post
https://www.linkedin.com/pulse/how-make-cluster-ha-proxmox-6xdebian-10-multipath-iscsi-mehmet-yeter