[Linux-cluster] Networking guidelines for RHCS across datacenters

brem belguebli brem.belguebli at gmail.com
Fri Jun 5 17:17:21 UTC 2009


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

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.


2009/6/5, Fajar A. Nugraha <fajar at fajar.net>:
> On Fri, Jun 5, 2009 at 4:22 PM, brem belguebli<brem.belguebli at 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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> Linux-cluster at redhat.com
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