Is it possible to have a stretched cluster (MNS) across 2 datacenters running
SQL?

For example, a SAN in each datacenter with replication, and 1 node located
in each site.

We are trying to design our new datacenter infrastructure, and our IT
Director believes there is a way to have 1 node in each site, each accessing
a local SAN which replicates it's content and using a MNS cluster.

I have searched around but cannot find any info. He is also suggesting we
use Win2k8, but I can't find any info on this sort of setup. We currently
have a mix of SQL 2k5/2000.

It is possible to have a "stretch" cluster, but not using Majority Node Set.
Since SQL needs a central data repository, using MNS for the cluster qourum
creates no benefit. There are not any native tools to implement a
geocluster (as it is properly called), but third-party vendors offer some
bolt-on solutions. If we are lucky, Linchi will chime in with some answers
here. He is the best resource I know for this information. NSI's
Doubletake has a geocluster offering as does EMC's SRDF (part of their
storage systems suite).

--
Geoff N. Hiten
Senior SQL Infrastructure Consultant
Microsoft SQL Server MVP






"daesimps" <daesimps (AT) discussions (DOT) microsoft.com> wrote

Sorry for the use of the term "stretched". I have been trying to correct the
director every time he uses that term, but it would seem it has rubbed off on
me!! :-)

Your reply seems to be along the same lines as my response to him, but you
know management. They always seem to know better than the Technical staff
they employ!

Thanks
Daesimps

"Geoff N. Hiten" wrote:

Well, if you are planning on a cluster that spans two geographically
separate data centers, your director is correct in that it is a stretched
cluster. 'Stretch clusters' or geo clusters are almost always vendor
specific. EMC has a product called SRDF/CE, standing for Cluster Enabler.
Basically, what it does is to have one or more nodes in each of the two data
centers, data is replicated synchronously at disk array level via SRDF, and
SRDF/CE creates an illusion to MSCS in that the storage appears to MSCS as a
single shared drive(s). So as far as MSCS is concerned, it's a regular
Microsoft failover cluster. For many companies, the problem is often the
requirement of having the VLAN spanning two different data centers and the
network folks often don't like that idea. Fortunately, in Win2K8 the same
VLAN requirement will be dropped.

That said, I'm not sure such a stretched cluster is the best solution for
whatever DR requirements you try to meet. It's complex and over too many
layers. If you don't have SRDF already, it requires putting in place an
expensive infrastructure. Even if you already have SRDF, SRDF/CE is separate
license. Often, you can meet your DR requirements with some other
approach(es).

Linchi

"daesimps" <daesimps (AT) discussions (DOT) microsoft.com> wrote

See. I told you he was the expert.

Thanks, Linchi.

--
Geoff N. Hiten
Senior SQL Infrastructure Consultant
Microsoft SQL Server MVP


"Linchi Shea" <linchi_shea (AT) NOSPAMml (DOT) om> wrote

Thanks for the info. We use HP Eva 6000 Storage equipment, so we'll have to
investigate if there is an equivalent to the EMC cluster enabler.


"Geoff N. Hiten" wrote:

On Dec 8, 7:51 am, daesimps <daesi... (AT) discussions (DOT) microsoft.com>
wrote:
What is your RTO and RPO? There are other options that are SQL
specific, including database mirroring, transactional replication, etc.