Disaster Recovery Implementations; Lan-Based Versus Internet-Based Applications; Host-Based Versus Storage-Based Data Mirroring - Novell BUSINESS CONTINUITY CLUSTERING 1.1 SP2 - ADMINISTRATION Administration Manual

Continuous availability of critical business systems is no longer a luxury, it is a competitive business
requirement.The Gartner Group estimates that 40% of enterprises that experience a disaster will go
out of business in five years, and only 15% of enterprises have a full-fledged business continuity
plan that goes beyond core technology and infrastructure.
The cost to the business for each one hour of service outage includes the following:
Income loss measured as the income-generating ability of the service, data, or impacted group
Productivity loss measured as the hourly cost of impacted employees
Recovery cost measured as the hourly cost of IT personnel to get services back online
Future lost revenue because of customer and partner perception

1.2 Disaster Recovery Implementations

Stretch clusters and cluster of clusters are two approaches for making shared resources available
across geographically distributed sites so that a second site can be called into action after one site
fails. To use these approaches, you must first understand how the applications you use and the
storage subsystems in your network deployment can determine whether a stretch cluster or cluster of
clusters solution is possible for your environment.
Section 1.2.1, "LAN-Based versus Internet-Based Applications," on page 14
Section 1.2.2, "Host-Based versus Storage-Based Data Mirroring," on page 14
Section 1.2.3, "Stretch Clusters vs. Cluster of Clusters," on page 15

1.2.1 LAN-Based versus Internet-Based Applications

Traditional LAN applications require a LAN infrastructure that must be replicated at each site, and
might require relocation of employees to allow the business to continue. Internet-based applications
allow employees to work from any place that offers an Internet connection, including homes and
hotels. Moving applications and services to the Internet frees corporations from the restrictions of
traditional LAN-based applications.
By using Novell exteNd Director portal services, iChain
applications, and data can be rendered through the Internet, allowing for loss of service at one site
but still providing full access to the services and data by virtue of the ubiquity of the Internet. Data
and services continue to be available from the other mirrored sites.

1.2.2 Host-Based versus Storage-Based Data Mirroring

For clustering implementations that are deployed in data centers in different geographic locations,
the data must be replicated between the storage subsystems at each data center. Data-block
replication can be done by host-based mirroring for synchronous replication over short distances up
to 10 km. Typically, replication of data blocks between storage systems in the data centers is
performed by SAN hardware that allows synchronous mirrors over a greater distance.
For stretch clusters, host-based mirroring is required to provide synchronous mirroring of the SBD
(split-brain detector) partition between sites. This means that stretch-cluster solutions are limited to
distances of 10 km.
14 BCC 1.1 SP2: Administration Guide for NetWare 6.5 SP8
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