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Re: [Linux-cluster] Networking guidelines for RHCS across datacenters



Hello,
 
We are long term HP ServiceGuard on HP-UX users and since a few months HP ServiceGuard on Linux (aka SGLX).
 
The first one (HP-UX) works by using their Cluster LVM (a clvmd-like daemon named cmlvmd on each node) allowing one node of the cluster to activate exclusively (vgchange -a e VGXX) on one node and use a non-clustered FS (vxfs) on top of the LV's.
 
The LV's are mirrored (a leg on each SAN array, one local and the other distant).
 
On Linux (SGLX) is a bit more tricky but when masterized it works well.
 
It relies on non-clustered LVM, with the LVM2 hosttags feature (HA-LVM described by RH) built on top of MD raid1 devices with a cluster module that guarantees the raid device to be consistent on one node at a time.
 
Unfortunately, HP just announced the discontinuation of SGLX, that's why we are looking towards RHCS to see if it can provide the same service, which doesn't seem to be obvious.
 
Concerning LVM mirroring with Clustered LVM, I hope it does or will.
 
The only thing I know about  LVM mirror is that, soon (maybe around RH5u5) it will support online resizing without having to break the mirror. 
 
Brem
   

 
2009/6/5, Fajar A. Nugraha <fajar fajar net>:
On Fri, Jun 5, 2009 at 4:22 PM, brem belguebli<brem belguebli gmail com> wrote:
> We are in the same setup, already doing "Geo-cluster" with other technos and
> we are looking at RHCS to provide us the same service level.

Usually the concepts are the same. What solution are you using? How
does it work, replication or real cluster?

> Let's consider this kind of setup, 2 datacenters far from each other by 1 ms
> delay, each hosting a SAN array, each of them connected to 2 SAN fabrics
> extended between the 2 sites.
>
> What reason would prevent us from building Geo-clusters without having to
> rely on a database replication mechanism, as the setup I would like to
> implement would also be used to provide NFS services that are disaster
> recovery proof.
>
> Obviously, such setup should rely on LVM mirroring to allow a node hosting a
> service to be able to write to both local and distant SAN LUN's.

Does LVM mirroring work with clustered LVM?

--
Fajar

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