GeoCluster - Windows from here to Timbuktu

Global Double-Take

Designing a Defense for Mobile Applications

Double-Take Software - which was founded to provide data replication for servers and their applications - has been transforming itself into a workload optimization and high availability software vendor. And like everyone else, Double-Take is trying to get into the virtualization game - not just to make money, but because servers are being virtualized and their virtual machines need a lot of the same resiliency that was originally provided for physical servers.

Like other geographic replication tools, Double-Take's GeoCluster software uses an IP network link to link source and target servers together, replicating data asynchronously. With this asynchronous link, servers can be geographically dispersed, and data replication can still happen over relatively-low-bandwidth, long-distance links - usually T1 lines among Double-Take's customer base.

GeoCluster, which runs atop Windows Clustering Service, adds a few tricks of its own. Cluster Service can span up to 16 nodes in a cluster, but requires the nodes to be linked to a storage area network. But using the data replication software that the company sells as a standalone product for Windows and Linux servers, GeoCluster allows each server to keep its own local copy of the data, which means you don't need to have identical servers in the cluster and you don't need to buy a SAN. Windows Cluster Service also is not made to span long distances. That is a function that Double-Take (as well as a number of other vendors) slap on top of Cluster Service to make some money.

Even with that, Cluster Service made it tough to do meaningful separation for servers, which you want to truly protect your data and applications. According to Bob Roudebush, director of solutions engineering at Double-Take, Windows Server 2008 has two important tweaks that make geographically distributed clusters more practical compared to setups running on Windows Server 2003, which had some issues. And the new GeoCluster Version 5.1 release from Double-Take takes advantage of them.

The first limitation in the clustering services that come with Windows Server 2003 was that nodes separated from each other geographically in a cluster still had to be in the same subnet on the corporate network. This forced network administrators to stretch a subnet address over the wide area network. This was both tricky and annoying. The heartbeat inside cluster services for Windows Server 2003 was hard-coded at 500 milliseconds.

This was problematic because depending on network traffic and distances, the latency between source and target machines could be in excess of 500 milliseconds, and when that happens, the replication link is broken. This limits geographic separation in most customers to on the order of miles and kilometers, which defeats the purpose of setting up a GeoCluster in the first place.

With the cluster services inside Windows Server 2008, Microsoft now lets the two machines linked together be on different subnets, and it also lets administrators set the timeout on the heartbeat. These changes make GeoCluster for Windows customers more relevant. Zane Adam, senior director of virtualization strategy at Microsoft, says that roughly one-third of the companies deploying Windows Server 2008 thus far have deployed it in clusters for high availability.

GeoCluster 5.1 is also aware of virtual machines running atop the Hyper-V hypervisor, and virtual machines can be replicated and failed over from one box to another, just like physical boxes do. GeoCluster is also aware of the quick migration feature that Microsoft puts in the Enterprise and Datacenter Editions of Windows Server 2008, which allows for a VM to be teleported around a network of machines that have shared storage. As with physical machines, the combination of GeoCluster, Hyper-V, and quick migration means that a SAN is not necessary. All the servers can use local storage because of the replication that GeoCluster is doing behind the scenes.

GeoCluster 5.1 supports Windows Server 2003 and Windows Server 2008, although given the limitations of the earlier Windows, this is obviously not where either Double-Take or Microsoft is focused. (Windows Server 2000 is not supported). Each node in a cluster needs to have its own GeoCluster license, which costs $4,940 a pop.

While Double-Take has data replication and high availability failover products for Linux, Roudebush says that at this time the company no plans to offer GeoCluster on any Linux. The commercial Linux distributions from Red Hat and Novell have had support for clustering for years, but the Double-Take for Linux product, which provides replication and failover on closely packed servers, only supports Red Hat Enterprise Linux 4 and 5. ®

The Power of One eBook: Top reasons to choose HP BladeSystem

More from The Register

next story
Apple fanbois SCREAM as update BRICKS their Macbook Airs
Ragegasm spills over as firmware upgrade kills machines
Attack of the clones: Oracle's latest Red Hat Linux lookalike arrives
Oracle's Linux boss says Larry's Linux isn't just for Oracle apps anymore
THUD! WD plonks down SIX TERABYTE 'consumer NAS' fatboy
Now that's a LOT of porn or pirated movies. Or, you know, other consumer stuff
EU's top data cops to meet Google, Microsoft et al over 'right to be forgotten'
Plan to hammer out 'coherent' guidelines. Good luck chaps!
US judge: YES, cops or feds so can slurp an ENTIRE Gmail account
Crooks don't have folders labelled 'drug records', opines NY beak
Manic malware Mayhem spreads through Linux, FreeBSD web servers
And how Google could cripple infection rate in a second
FLAPE – the next BIG THING in storage
Find cold data with flash, transmit it from tape
prev story


Designing a Defense for Mobile Applications
Learn about the various considerations for defending mobile applications - from the application architecture itself to the myriad testing technologies.
How modern custom applications can spur business growth
Learn how to create, deploy and manage custom applications without consuming or expanding the need for scarce, expensive IT resources.
Reducing security risks from open source software
Follow a few strategies and your organization can gain the full benefits of open source and the cloud without compromising the security of your applications.
Boost IT visibility and business value
How building a great service catalog relieves pressure points and demonstrates the value of IT service management.
Consolidation: the foundation for IT and business transformation
In this whitepaper learn how effective consolidation of IT and business resources can enable multiple, meaningful business benefits.