Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
On Tue, Nov 17, 2009 at 4:42 AM, Lars Ellenberg <lars.ellenberg at linbit.com> wrote: > On Sun, Nov 15, 2009 at 01:08:30AM -0500, Jiann-Ming Su wrote: >> Don't know if this has been discussed before, but it seems like with >> 8.3's dual primary support, it's possible to set up a 3-node, all >> active drbd cluster. >> >> Each node would be dual primary with each other node. Node A would >> form drbd0 with node B and drbd1 with node C. Node B would have drbd0 >> with A and drbd2 with C. And, C would have drbd1 with A and drbd2 >> with B. >> >> Then you can use software raid to create md0 on each node with its >> respective drbd devices. >> >> Noce A: md0 (drbd0, drbd1) >> Node B: md0 (drbd0, drbd2) >> Node C: md0 (drbd1, drbd2) >> >> Then format md0 on each node with a cluster filesystem like ocfs2 with >> each node as a member of the cluster. >> >> Do the drbd experts here have any thoughts on how this idea would go >> horribly wrong? Thanks for any input and feedback. > > > A-MD(A-DRBD0(A-sdx), A-DRBD1(A-sdy)) > B-MD(B-DRBD0(B-sdx), B-DRBD2(B-sdy)) > C-MD( C-DRBD1(C-sdx), C-DRBD2(C-sdy)) > > > So you write block N on A-MD. > It will hit A-DRBD0, and A-DRBD1, > which will hit local disks A-sdx, A-sdy, > and via DRBD replication B-sdx, and C-sdx. > > Still with me? > Great. > > Now, you want to read that block N on B, > which decides in its read balancing path to fetch > block N from B-sdy. > > It will surely get _some_ data from there, > but certainly not the data you just wrote on A-MD. > > To summ it up in one word: > DON'T. > Thanks for the insight! So there's no easy way to verify a write has sync'd across all the nodes? For the application I want to use this type of 3-node config on, I think I'm willing to sacrifice the performance for the data replication. -- Jiann-Ming Su "I have to decide between two equally frightening options. If I wanted to do that, I'd vote." --Duckman "The system's broke, Hank. The election baby has peed in the bath water. You got to throw 'em both out." --Dale Gribble "Those who vote decide nothing. Those who count the votes decide everything.” --Joseph Stalin