Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
On 2007.12.18, at 15:52, Lars Ellenberg wrote: > On Mon, Dec 17, 2007 at 10:55:02AM +0100, Martin Gombac wrote: >> On 2007.12.13, at 18:24, Martin Gombac wrote: >> >>> On 2007.12.13, at 17:42, Florian Haas wrote: >>> >>>> On Thursday 13 December 2007 13:45:47 Martin Gombac wrote: >>>>> Hi, >>>>> >>>>> ..... >>>>> without synchronized drbd resources (amongst other things). >>>>> >>>>> My question is this: >>>>> How can i make one node take over all resources if local crossover > > you don't want to. But it do. :-) See below why. > > if your lan connection dies, > and your lan connection was your replication link, > then you don't have replication anymore, > and so you would go online with non-current data. Couple of seconds old data would come up on the second node, i agree. But it's way better than scenario described below: So both nodes have secondary/slave drbd resource out of sync. Since my replication link probably died due to a broken network card i have to take the node with broken card down. In this case the second (healthy) node would come up with _really_ out of date data for second resource or not at all if i used dopd. Which means we don't have a true fail-over cluster and would have unnecessary downtime. But we use clustering in the first place to avoid downtime. (I also have other applications communicating over this link, but can easily make them use WAN.) > > if currently your LAN connection is a direct "crossover cable", > why would you think any clients would benefit from failing over? > There would very little downtime (if it fails over to healthy node), no outdated drbd resources (oppose to one outdated if it doesn't failover) and as soon as i fix network card, synchronization would be auto-magic. Loosing a couple of seconds of data is in my opinion much better than having at least half hour downtime or more when i shut down broken server. > if you change to a switched LAN, and add a ping node, > why do you think any clients would benefit from that? > We would know on which node the network failed and on which it works so fail-over would be in the right direction. Later on i would fix the node with broken network card or whathever plug it back in and it would come back to cluster (sync and all). Clients would benefit by not having any downtime, like it would be using dopd. > how can you be sure what component failed, > local NIC, cables, remote NIC, switch, driver, ...? > If the switch or ping node failed, both nodes would detect that and no fail-over would happen. I would replace switch and synchronization would start auto-magically. If there would be a failure on local network interface, cable or driver one node would still get the pings back so we would know on which side it failed and the healthy node would take over thanks to heartbeat. > what problem are you trying to solve? > I mean not "failing over when the LAN link dies". > please zoom out a little. > To have as little downtime as possible if replication link fails. I think i explained this a couple of times by now. If data get's outdated on one node and the other has to be taken down for repairs => service offline. > from my point of view, it makes no sense to trigger a failover > because the replication link dies. it would even be harmful. > so don't do that. > What should i do then? Just take offline one node at the time (and half of the services with it) and take my time to repair it? Why do i even bother setting up a cluster then? I have all my clusters set up till now like you described, no fail- over when sync link dies. But recently on one of my clusters I have had a problem i described (broken network card for one sync node) and it led to downtime. My client now states that, if fail-over in this case of a network card failure didn't happen, i have _not_ set them up fail-over cluster. I guess we all know how annoying clients can be at times. So for future installs and the one i'm doing now i want it to be bulletproof. :-) > -- > : Lars Ellenberg http://www.linbit.com : > : DRBD/HA support and consulting sales at linbit.com : > : LINBIT Information Technologies GmbH Tel +43-1-8178292-0 : > : Vivenotgasse 48, A-1120 Vienna/Europe Fax +43-1-8178292-82 : > __ > please use the "List-Reply" function of your email client. > _______________________________________________ > drbd-user mailing list > drbd-user at lists.linbit.com > http://lists.linbit.com/mailman/listinfo/drbd-user