Evaluating Different Disaster Scenarios

Before a backup and disaster recovery plan can be formulated, IT managers and administrators should meet with the business owners to discuss and decide on which types of failures or disasters should be planned for. This section of the chapter provides a high-level description of common disaster scenarios to consider. Of course, planning for every disaster scenario is nearly impossible or, more commonly, will exceed an organization’s backup and recovery budget, but discussing the likelihood of each scenario and evaluating how the scenario can impact the business is necessary.

Physical Disaster
A physical disaster is anything that can keep employees or customers from reaching their desired office or store location. Examples include natural disasters such as floods, fires, earthquakes, hurricanes, or tornadoes that can destroy an office. A physical disaster can also be a physical limitation, such as a damaged bridge or highway blockage caused by a car accident. When only physical access is limited or restricted, a remote access solution could reestablish connectivity between users and the corporate network.

Power Outage or Rolling Blackouts
Power outages can occur at any time unexpectedly. Some power outages are caused by bad weather and other natural disasters, but other times they can be caused by high power consumption that causes system overloads. When power systems are overloaded, rolling blackouts may occur. A rolling blackout is when a power company shuts off power to certain power subscribers or areas of service, so that it maintains power to critical services, such as fire departments, police departments, hospitals, and traffic lights. The rolling part of rolling blackouts is that the blackout is managed; after a predetermined amount of the time, the power company will shut down a different power grid and restore power to a previously shutdown grid. Of course, during power outages, many businesses are unable to function because the core of their work is conducted on computers or even telephone systems that require power to function.

Network Outage
Organizations that share data and applications between multiple offices and require access to the Internet as part of their daily business operations are susceptible to network outages that can cause severe loss of employee productivity and possibly revenue. Network outages can affect just a single computer, the entire office, or multiple offices depending on the cause of the outage. IT staff must take network outages into consideration when creating the backup and recovery plans.

Hardware Failures
Hardware failures seem to be the most common disaster encountered and coincidentally are the most common type of problem organizations plan for. Server hardware failures include failed motherboards, processors, memory, network interface cards, network cables, fiber cables, disk and HBA controllers, power supplies, and, of course, the hard disks in the local server or in a storage area network (SAN). Each of these failures can be dealt with differently, but to provide system- or server-level redundancy, key services should be deployed in a redundant cluster configuration, such as is provided with Windows Server 2008 R2, Enterprise Edition Failover Clustering, or Network Load Balancing (NLB).

Hard Drive Failure
Hard drives are indeed the most common type of computer- and network-related hardware failure organizations have to deal with. Windows Server 2008 R2 supports hot-swappable hard drives and two types of disks: basic disks, which provide backward compatibility, and dynamic disks, which allow software-level disk arrays to be configured without a separate hardware-based disk array controller. Also, both basic and dynamic disks, when used as data disks, can be moved to other servers easily to provide data or disk capacity elsewhere if a system hardware failure occurs and the data on these disks needs to be made available as soon as possible. Windows Server 2008 R2 also contains tools to provision, connect, and configure storage located on a SAN and can easily mount VHD files as operating system disks using Disk Manager or diskpart.

Software Corruption
Software corruption can occur at many different levels. Operating system files could be corrupted, antivirus software can interfere with the writing of a file or database causing
corruption, or a new application or driver installation could overwrite a critical file leaving a system unstable or in a failed state. Also, more commonly found in today’s networks, a security, application, or system update conflicts with an existing application or service causing undesirable issues.

Source of Information : Sams - Windows Server 2008 R2 Unleashed

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