Windows Server 2008 R2 Unleashed (231 page)

balancing and device failover. Load balancing is the process of spreading requests across

multiple devices to keep individual device load at an acceptable level. Failover is the

process of moving services offered on one device to another upon device failure, to main-

tain availability. Common scenarios for creating fault-tolerant IP networks can include,

but are not limited to, the following:

.
Acquiring multiple network connections between the data center and the

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Internet—
This includes using different Internet service providers and, hopefully,

each of the connections is not connected to the same external telco box on the

street as this becomes the single point of failure if hit by a car, truck, or cut off from

communications.

.
Deploying multiple and redundant firewalls, virtual private networks

(VPNs), and network routers that will failover to one another—
This usually

involves software or hardware configurations that allow each of the devices to

communicate with one another to detect failures. These devices, when deployed in

redundant configurations, can be leveraged in an active/passive configuration where

only a single primary device is used and the secondary device only comes online

when the primary fails. Alternatively, in many cases these devices can be used in an

active/active configuration that disperses or distributes the load and requests across

each device and when a single device fails, the remaining device handles the entire

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load.

.
Deploying critical servers with multiple network adapters connected to

separate network switches—
This allows a server to be connected and available on

different switches in case a single network card in the server fails or if the port or the

entire network switch or blade fails.

.
Deploying hardware-based NLB devices—
Many network switches, routers, and

certain devices created just for this purpose can provide some, if not all, of the func-

tionality included in Windows Server 2008 R2 NLB. This, of course, might be the

best choice for load balancing at the network level when organizations deploy and

support systems other than Windows Server 2008 R2 and when they also need to

load-balance network devices, such as firewalls and VPN devices.

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.
Deploying servers with multiple network adapters using third-party network

teaming software—
This configuration uses third-party software installed and con-

figured on a server to create a new virtual network adapter that is used to provide

access to the server system through a single or all of the physical network adapters

on the server that are part of this configuration. Windows Server 2008 R2 supports

teamed network adapters as long as the drivers and software are certified to work

with Windows Server 2008 R2.

NOTE

If the Windows Server 2008 R2 system utilizes iSCSI storage, the network adapters

designated for iSCSI communications are not supported on teamed network adapters.

Designing Fault-Tolerant Server Disks

Many Windows Server 2008 R2 systems that will be used for NLB or failover clusters are

deployed with local disk storage. The local disks commonly store the operating system

files as well as the necessary service or application files. Each system that will participate

in a cluster should have the local disks and volumes configured exactly the same, includ-

ptg

ing drive letters and any mount point assignments. When local disks are used to provide

the operating system and application or service core files, the local disks should be

deployed using redundant, fault-tolerant configurations. There are mainly two different

ways to add fault tolerance to the local disks in a Windows Server 2008 R2 system. The

first is creating redundant arrays of inexpensive disks (RAID) using disk controller configu-

ration utilities (also known as hardware-level RAID), and the second is creating RAID

volumes using dynamic disks using the Disk Management console from within the operat-

ing system (known as software-level RAID).

Using two or more disks, different RAID-level arrays can be configured to provide fault

tolerance that can withstand disk failures and still provide uninterrupted disk access.

Implementing hardware-level RAID configured, stored, and managed by the system’s disk

controllers is preferred over the software-level RAID configurable within Windows Server

2008 R2. Windows Server 2008 R2 dynamic disk mirrored and RAID-5 volumes are

managed by the system and add some load to the system. Additionally, another good

reason to provide hardware-level RAID is that the configuration of the disks does not

depend on the operating system, which gives administrators greater flexibility when it

comes to recovering server systems and performing upgrades. For more information on

disk configuration options, refer to Chapter 28 of this book. For detailed information on

how to best configure RAID arrays using local disk controllers, refer to the manufacturer’s

documentation.

As a best practice, Windows Server 2008 R2 can be deployed with the operating system

disks stored on RAID-1, or mirrored, disks and presented to the operating system as the

“C” volume. A second volume in the system can be used to store application data and files

and, when possible, this data should be placed on different redundant disks or at least on

separate volumes to prevent impact to the space available in the operating system volume.

Windows Server 2008 R2 Clustering Technologies

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Increasing Service and Application Availability

A service and/or application’s reliability is greatly dependent on the underlying software

code, the hardware the system is running on, and how it interacts with the host operating

system. Windows Server 2008 R2 is a very stable platform partly because third-party appli-

cations and services must use only the system files provided by Microsoft when interact-

ing with the operating system and the system hardware. Furthermore, when third-party

services and applications require additional drivers, these drivers must be certified for

Windows Server 2008 R2 and the drivers must be digitally signed by the Windows Quality

Hardware labs to ensure the highest reliability. Administrators can disable the strict device

driver signing requirements, but on failover clusters, this would place the system in an

unsupported configuration and is not advisable. Remember that the only reason to deploy

failover clusters or NLB clusters is to provide high availability or very scalable services;

deploying systems using unsigned or untested drivers can reduce the overall reliability of

each system and the entire cluster.

Windows Server 2008 R2 Clustering Technologies

Windows Server 2008 R2 provides two clustering technologies, which are both included

on the Enterprise and Datacenter Editions. Clustering is the grouping of independent

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server nodes that are accessed and viewed on the network as a single system. When a

service and/or application is run from a cluster, the end user can connect to a single

cluster node to perform his work, or each request can be handled by multiple nodes in the

cluster. In cases where data is read-only, the client might request data from one server in

the cluster and the next request might be made to a different server and the client would

never know the difference. Also, if a single node on a multiple node cluster fails, the

remaining nodes will continue to service client requests and only the clients that were

originally connected to the failed node may notice either a slight interruption in service,

or their entire session might need to be restarted depending on the service or application

in use and the particular clustering technology that is in use for that cluster.

The first clustering technology provided with Windows Server 2008 R2, Enterprise and

Datacenter Editions is failover clustering. Failover clusters provide system fault tolerance

through a process called failover. When a system or node in the cluster fails or is unable to

respond to client requests, the clustered services or applications that were running on that

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particular node are taken offline and moved to another available node where functionality

and access are restored. Failover clusters, in most deployments, require access to shared

data storage and are best suited, but not necessarily limited to, the deployment of the

following services and applications:

.
File services—
File services deployed on failover clusters provide much of the same

functionality a standalone Windows Server 2008 R2 system can provide, but when

deployed as clustered file services, a single data storage repository can be presented

and accessed by clients through the currently assigned and available cluster node

without replicating the file data.

.
Print services—
Print services deployed on failover clusters have one main advan-

tage over a standalone print server: If the active print server fails, each of the shared

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printers is made available to clients using another designated print server in the

cluster. Although deploying and replacing printers to computers and users is easily

managed using Group Policy deployed printers, when standalone print servers fail,

the impact can be huge, especially when servers, devices, services, and applications

that cannot be managed with group policies access these printers.

.
Database services—
When large organizations deploy line-of-business applications,

e-commerce, or any other critical services or applications that require a back-end

database system that must be highly available, deploying database services on

failover clusters is the preferred method. Also, in many cases configuring enterprise

database services can take hours and the size of the databases, indexes, and logs can

be huge, so deploying database services on a standalone system encountering a

system failure may results in several hours of undesired downtime during repair or

restore, instead of quick recovery as with a failover cluster.

.
Back-end enterprise messaging systems—
For many of the same reasons as cited

previously for deploying database services, enterprise messaging services have

become critical to many organizations and are best deployed in failover clusters.

.
Hyper-V virtual machines—
As many organizations move toward server consolida-

tion and conversion of physical servers to virtual servers, providing a means to also

maintain high availability and reliability has become even more essential when a

ptg

single physical Hyper-V host has several critical virtual machines running on it.

The second Windows Server 2008 R2 clustering technology is Network Load Balancing

(NLB), which is best suited to provide fault tolerance for front-end web applications and

websites, Remote Desktop Services Session Host server systems, VPN servers, streaming

media servers, and proxy servers. NLB provides fault tolerance by having each server in

the cluster individually run the network services or applications, removing any single

points of failure. Depending on the particular needs of the service or application deployed

on an NLB cluster, there are different configuration or affinity options to determine how

clients will be connected to the back-end NLB cluster nodes. For example, on a read-only

website, client requests can be directed to any of the NLB cluster nodes; during a single

visit to a website, a client might be connected to different NLB cluster nodes. As another

example, when a client attempts to utilize an e-commerce application to purchase goods

or services provided through a web-based application on an NLB cluster, the client session

should be initiated and serviced by a single node in the cluster, as this session will most

likely be using Secure Sockets Layer (SSL) encryption and will also contain specific session

data, including the contents of the shopping cart and the end-user specific information.

NOTE

Microsoft does not support running failover clusters and Network Load Balancing on

the same Windows Server 2008 R2 system.

Windows Server 2008 R2 Clustering Technologies

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Windows Server 2008 R2 Cluster Terminology

Before failover or NLB clusters can be designed and implemented, the administrator

deploying the solution should be familiar with the general terms used to define the clus-

tering technologies. The following list contains the many terms associated with Windows

Server 2008 R2 clustering technologies:

.
Cluster—
A cluster is a group of independent servers (nodes) that are accessed and

presented to the network as a single system.

.
Node—
A node is an individual server that is a member of a cluster.

.
Cluster resource—
A cluster resource is a service, application, IP address, disk, or

network name defined and managed by the cluster. Within a cluster, cluster