On Sat, 7 Jul 2018 16:28:49 +0200 Gianluca Cecchi <gianluca.cec...@gmail.com> wrote:
> Hello, > I'm testing a virtual rhcs cluster based on 4 nodes that are CentOS > 7.4 VMs. So the stack is based on Corosync/Pacemaker > I have two oVirt hosts and so my plan is to put two VMs on first host > and two VMs on the second host, to simulate a two sites config and > site loss, before going to physical production config. > Incidentally the two hypervisor hosts are indeed placed into different > physical datacenters. > So far so good. > I decided to use OVN for the intracluster dedicated network > configured for corosync (each VM has two vnics, one on production lan > and one for intracluster). > I detected that the cluster worked and formed (also only two nodes) > only if the VMs run on the same host, while it seems they are not > able to communicate when on different hosts. Ping is ok and an > attempt of ssh session between them on intracluster lan, but cluster > doesn't come up So after digging in past mailing list mails I found > this recent one: > https://lists.ovirt.org/archives/list/users@ovirt.org/thread/RMS7XFOZ67O3ERJB4ABX5MGXTE5FO2LT/ > > where the solution was to set 1400 for the MTU of the interfaces on > OVN network. > It seems it resolves the problem also in my scenario: > - I live migrated two VMs on the second host and rhcs clusterware > didn't complain > - I relocated a resource group composed by several LV/FS, VIP and > application from VM running on host1 to VM running on host2 without > problems. > There will be a new feature [1][2] about propagating the MTU of the logical network into the guest. In ovirt-4.2.5 the logical network MTU <= 1500 will be propagated for clusters with switch type OVS and linux bridge, and MTU > 1500 will be propagated only for clusters with switch type linux bridge, if the requirements [3] are fulfilled in oVirt >= 4.2.5. OVS clusters will work for MTU > 1500 latest in oVirt 4.3. In this new feature a new default config setting "MTU for tunneled networks" is introduced, which will be set initially to 1442. > So the question is: can anyone confirm what are guidelines for > settings vnics on OVN? In the context of oVirt, I am only aware of [1] and [4]. Starting from oVirt 4.1 you can activate the OVN's internal dhcp server by creating a subnet for the network [4]. The default configuration will offer a MTU of 1442 to the guest, which is optimal for GENEVE tunneled networks over physical networks with a MTU of 1500. > Is there already a document in place about MTU > settings for OVN based vnics? There are some documents about MTU in OpenStack referenced in [1]. > Other particular settings or > limitations if I want to configure a vnic on OVN? > libvirt's network filters are not applied to OVN networks, so you should disable network filtering in oVirt's vNIC profile. This is tracked in [5]. [1] https://ovirt.org/develop/release-management/features/network/managed_mtu_for_vm_networks/ [2] https://github.com/oVirt/ovirt-site/pull/1667 [3] https://ovirt.org/develop/release-management/features/network/managed_mtu_for_vm_networks/#limitations [4] https://github.com/oVirt/ovirt-provider-ovn/#section-dhcp [5] https://bugzilla.redhat.com/show_bug.cgi?id=1502754 > Thanks, > > Gianluca _______________________________________________ Users mailing list -- users@ovirt.org To unsubscribe send an email to users-le...@ovirt.org Privacy Statement: https://www.ovirt.org/site/privacy-policy/ oVirt Code of Conduct: https://www.ovirt.org/community/about/community-guidelines/ List Archives: https://lists.ovirt.org/archives/list/users@ovirt.org/message/LZXNYHK554BCVHAXG2JXJ6AG3TU5DK4Y/
