[ovirt-users] Re: iSCSI multipath with separate subnets... still not possible in 4.4.x?

I think there's a misunderstanding behind the name, what happens is the following: When you deploy the hosted-engine you can choose only one target and path probably, so it uses the "default" interface, this is also true when you run a scan/discovery. As example, if using a standard iSCSI configuration (best practice is also having a different network switches, etc.. which i show in this example, but it works well even if you don't have), you will probably have two interfaces, each in his own Fault Domain, so let's say we have eth3 as FD1 and eth4 as FD2. Subnets: FD1 = 192.168.100.0/24 FD2 = 192.168.200.0/24 You will then create a logical network for each of those Fault Domains, so FD1 and FD2, make sure those are only attached and are not marked as VM network and are not "Required". After that, you will have to attach those logical networks to the hosts and configure their IP. For example on host1: We attach FD1 to eth3 and give it 192.168.100.11/24 We attach FD2 to eth4 and give it 192.168.200.11/24 Note that i did not specify any gateway, It's a simple Layer2 configuration. You will have to do this for each host (you can use ansible for automation which makes it very simple). After you have attached you first Storage Domain using iSCSI and did the procedure above you will under the Datacenter a new Tab named "iSCSI Multipathing" the name is confusing because it does not control the Multipath, configuration of the Multipath should be done by referencing to the vendor best practice and configure it under "/etc/multipath/conf.d" because the VDSM override /etc/multipath.conf In the "iSCSI Multipathing" section you will need to add those two Fault Domains. So for FD1 you will need to select the logical network we created earlier named "FD1" and then select the appropriate targets related to it only!, do the same for FD2. What happens behind the scene is that VDSM configure iSCSI (oVirt/RHEL uses libiscsi). You can observe that two interfaces were created, eth3 and eth4: "iscsiadm -m iface" Then look at the sessions: "iscsiadm -m session" Easiest way around is just seeing what was created in the "/var/lib/iscsi" folder: "find /var/lib/iscsi" You will see how VDSM configured iSCSI to interact with the targets, it tells it to use those specific interfaces to those specific targets. you can observe a session "iscsiadm -m session -r1 -P3" to get more details. So what really happened now is that VDSM will take care of making sure iSCSI works on each host, it will automatically login to the targets using those interfaces. I do agree the name "Multipathing" is confusing.