On Tue, 01 Nov 2011 09:03:41 -0400 (EDT), Bob Peterson <rpeterso@xxxxxxxxxx> wrote: > ----- Original Message ----- > | Which one is not true "I had used common storage" or "On both the > | nodes > | data is not in sync" - if it is a common storage the data is the > | same? > | > | if you are using GFS2 without a cluster and dlm locking i.e. > | local_locking > | then it is possible both to be true > (snip) > | GFS2 has nothing to do with syncing the data between two storages - > | if > | that's what you are after, check DRBD > | > | if you are using improperly configured GFS2 on a shared storage i.e. > | without cluster and dlm it is no different than any other local > | filesystem > | and corruption is guaranteed on simultaneous use > > Hi, > > IMHO, the most important things to bear in mind here are: > > (1) The job of GFS2 is to keep the file system _metadata_ consistent > between nodes in the cluster. > (2) It does _not_ keep DATA within the files consistent within the > cluster: that's the job of the application. > (3) If the application is not cluster-aware (i.e. one instance of > mysql doesn't know about another instance in the cluster) they > will trounce each other's updates, making the data inconsistent. > (4) The general rule is: If two instances of an app can run on the > same computer, in general it will work properly without data > corruption. But if one computer is not allowed to run two > instances of the same app, in general it will not work properly. > (5) With clustering you can essentially think of it this way: it > makes multiple computers run an app as if they were running > multiple instances on the same computer. Almost like forcing > the app to run two instances on the same computer (although > that's not at all what really happens). Multiple instances > on the same machine will use some kind of locking mechanism, > like posix locks, to maintain data integrity. > (6) Many apps are written with clustering in mind and there > may be special "clustered" versions of apps, like mysql. > It's best to check with the app experts or clustering experts > or the cluster FAQ before implementing this kind of thing. > > So bottom line: You can't run two copies of regular mysql on the > same box (unless it's a special cluster-aware mysql) without conflicts > so you can't run two copies of regular mysql in a cluster without > data corruption, because they are not cluster-aware. > I agree with all said, but it is possible to run more than one instance of regular mysql on the same box. I run 3 (slave of master 1, slave of master 2 and combined RO export) instances (on the same machine), using the same data without problems, but you need to define 'external-locking' which slows them down running two instances in a cluster from shared storage is possible, but much slower and not a solution. > Regards, > > Bob Peterson > Red Hat File Systems > > -- > Linux-cluster mailing list > Linux-cluster@xxxxxxxxxx > https://www.redhat.com/mailman/listinfo/linux-cluster -- Linux-cluster mailing list Linux-cluster@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/linux-cluster
