JR wrote:
> It has nothing to do with VMs at all. We're talking about the storage block > device (DRBD) being accessible on both nodes simultaneously: > http://www.drbd.org/users-guide/s-enable-dual-primary.html I understand > "active-active" and "dual-primary" is a common term applicable in many > places,but to be clearly, just talking about the configuration options in > drbd.conf: > net { > allow-two-primaries; > } > startup { > become-primary-on both; > } > The reason you make it active-active on both nodes is because with > Live-Migration the VM does exist simultaneously on both nodes for a brief > period of > time as the memory pages/state are > migrated over and both access the block device simultaneously yet in a > synchronized manner through the underlying HyperVisor. Indeed, there is a > mechanism in place for synchronization as your >surmised there must be. > Don't I need a cluster aware FS for that short period of time when both are > running ? What mechanism for synchronization do you mean ? > Can I realise the Live migration with cluster tools, or with KVM tools ? If I > use KVM tools, don't they interfere with the HA-Software ? > They are never "both running" at the same time: though they may exist on both > hosts at the same time, one VM instance will stop before the copy of this > > VM instance starts from where the original stopped. > How familiar are you with live migration? > http://www.linux-kvm.org/wiki/images/5/5a/KvmForum2007$Kvm_Live_Migration_Forum_2007.pdf > The key point of > LiveMigration is that the VM is copied to another physical host while > running, after which the original VM is paused, then dirty pages that changed > since the initial page copy are synchronized over quickly, and then it does a > quick hand off from one physical to host to the other (MAC addresses, etc) > before unpausing the recently sync'd VM on the new host. Check out pages 4-9 > in the PDF above for a more detailed description of this process. While > the VM exists on 2 physical hosts for a brief moment during this process, the > HyperVisor or KVM makes sure only 1 copy of the VM is active at a time. > The short answer to your "do I need a cluster aware FS" is: no. You need > block-level synchronization, in your case KVM assures this during a live- > migration. These are some fairly semantic low-level details, I just wanted > to be precise in what was actually happening here. DRBD's "allow-two- > primaries;" is required for LiveMigration. Live Migration sounds very interesting. I think i will create a dual-primary solution. Concerning the live migration: Are they performed with HA-Tools in pacemaker, or with KVM-Tools ? Bernd _______________________________________________ drbd-user mailing list [email protected] http://lists.linbit.com/mailman/listinfo/drbd-user
