HP Serviceguard Extended Distance Cluster for Linux A.12.00.00 Deployment Guide, March 2014

2 Building an Extended Distance Cluster Using Serviceguard
and Software RAID
Simple Serviceguard clusters are usually configured in a single data center, often in a single room,
to provide protection against failures in CPUs, interface cards, and software. Extended Serviceguard
clusters are specialized cluster configurations, which allow a single cluster to extend across two
separate data centers for increased disaster recovery. Depending on the type of links employed,
distances of up to 100 kms between data centers can be achieved.
This chapter discusses several types of extended distance cluster that use basic Serviceguard
technology with software mirroring (using MD Software RAID) and Fibre Channel. Both two data
center and three data center architectures are illustrated.
2.1 Typical Configuration of an Extended Distance Clusters
In an extended distance cluster, for data replication, the MD (Multiple Device) driver or VxVM
mirroring is used. For more information about VxVM mirroring, see Veritas Storage Foundation
Administrator's Guide available at https://sort.symantec.com/documents/doc_details/sfha/6.0.1/
Linux/ProductGuides. Using the MD kernel driver, you can configure RAID 1 (mirroring) in your
cluster. In a dual data center setup, to configure RAID 1, one LUN from a storage device in data
center 1 is coupled with a LUN from a storage device in data center 2. As a result, the data that
is written to this MD device is simultaneously written to both devices. A package that is running
on one node in one data center has access data from both storage devices.
The two recommended configurations for the extended distance cluster are both described below.
Figure 3 Extended Distance Cluster
In the above configuration the network and FC links between the data centers are combined and
sent over common DWDM links. Two DWDM links provide redundancy. When one of them fails,
the other may still be active and may keep the two data centers connected. Using the DWDM link,
clusters can now be extended to greater distances which were not possible earlier due to limits
2.1 Typical Configuration of an Extended Distance Clusters 15