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Creating a Fault-Tolerant Environment

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In This Chapter

  • Optimizing Disk Management for Fault Tolerance

  • Maximizing Redundancy and Flexibility with Distributed File System

  • Simplifying Fault Tolerance with Volume Shadow Copy

  • Optimizing Disk Utilization with Remote Storage

  • Optimizing Clusters to Simplify Administrative Overhead

  • Leveraging Network Load Balancing for Improved Availability

  • Realizing Rapid Recovery Using Automated System Recovery (ASR)

Best Practices

  • Setting Up DFS

  • DFS Replication

  • Using Volume Shadow Copy Service (VSS)

  • Using Remote Storage

  • Configuring Clusters

  • Network Load Balancing

Because more and more businesses rely on constant and uninterrupted access to their IT network resources, many technologies have been created to help ensure continuous uptime of servers and applications. Windows Server 2003 is inline with these new technologies to meet the demands of the modern business model that seeks to provide a fault-tolerant network environment where unexpected downtime is a thing of the past. By combining Windows Server 2003 technologies with the appropriate hardware and general best practices, IT organizations can realize both file-level and system-level fault tolerance to maintain a high level of availability for their business-critical applications and network services.

This chapter highlights the features available in Windows Server 2003 that target fault tolerance and provides best practices for their implementation of and application to the IT environment. On the file-system side, in addition to proper disk management and antivirus protection, Windows Server 2003 provides Distributed File System (DFS), Volume Shadow Copy (VSC), and Remote Storage technologies. Related to system-level fault tolerance, Windows Server 2003 includes the Microsoft Cluster Service (MSCS) and Network Load Balancing (NLB) technologies to provide redundancy and failover capabilities.

Optimizing Disk Management for Fault Tolerance

System administrators have long since relied on Redundant Arrays of Inexpensive Disks (RAID) technologies to provide levels of fault tolerance for their server disk resources. And though the technology is a familiar mainstay in server management, its importance should not be overlooked. There are a couple of ways to leverage RAID to optimize disk management in Windows Server 2003. The first is creating RAID disks using disk controller configuration utilities, and the second is creating the RAID disks using dynamic disk configuration from within the Windows Server 2003 operating system.

Hardware-based RAID Solutions

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. Hardware-based RAID is achieved when a separate RAID disk controller is used to configure and manage the disks participating in the RAID array. The RAID controller stores the information on the array configuration, including disk membership and status.

Implementing hardware-level RAID configured and stored on the disk controller is preferred over the software-level RAID configurable within Windows Server 2003 Disk Management because the Disk Management and synchronization processes in hardware-level RAID are offloaded to the RAID controller. With Disk Management and synchronization processes offloaded from the RAID controller, the operating system will perform better overall.

Another reason to provide hardware-level RAID as a best practice is that the configuration of the disks does not depend on the operating system. This gives administrators greater flexibility when it comes to recovering server systems and performing upgrades.

Because there are many hardware-based RAID solutions available, it is important to refer to the manufacturer's documentation on creating RAID arrays to understand the particular functions and peculiarities of the RAID disk controller in use.

Using Dynamic Disk RAID Configurations

Windows Server 2003 supports two types of disks: basic and dynamic. Basic disks are backward-compatible, meaning that basic partitions can be accessed by previous Microsoft operating systems such as MS-DOS and Windows 95 when formatted using FAT; and when formatted using NTFS, Windows NT, Windows 2000, and Windows .NET Server 2003 can access them.

Dynamic disks are managed by the operating system and provide several configuration options, including software-based RAID sets and the capability to extend volumes across multiple disks. Though there are several configuration options, including spanned and stripped volumes, the only really fault tolerant dynamic disk configurations involve creating mirrored volumes (RAID 1) or RAID 5 volumes as described in the following list:

  • Mirrored Volume (RAID 1). Mirrored volumes require two separate disks, and the space allocated on each disk must be equal. Mirrored sets duplicate data across both disks and can withstand a single disk failure. Because the mirrored volume is an exact replica of the first disk, the space capacity of a mirrored set is limited to half of the total allocated disk space.

  • RAID 5 Volume. Software-based RAID 5 volumes require three or more disks and provide faster read/write disk access than a single disk. The space or volume provided on each disk of the RAID set must be equal. RAID 5 sets can withstand a single disk failure and can continue to provide access to data using only the remaining disks. This capability is achieved by reserving a small portion of each disk's allocated space to store data parity information that can be used to rebuild a failed disk or to continue to provide data access.

Using the Disk Management MMC

Most disk-related administrative tasks can be performed using the Disk Management MMC snap-in. This tool is located in the Computer Management console, but the standalone snap-in can also be added in a separate Microsoft Management Console window. Disk Management is used to identify disks, define disk volumes, and format the volumes.

New Feature in the Windows Server 2003 Disk Management Console

A new feature in the Windows Server 2003 Disk Management console enables administrators to also manage disks on remote machines.

To use the Disk Manager to create a software-based RAID, the disks that will participate in the array must first be converted to dynamic disks. This is a simple process by which the administrator right-clicks on each disk in question and chooses Convert to Dynamic, as shown in Figure 22.1.

Figure 22.1Figure 22.1 Convert basic disks to dynamic.

The system will require a reboot to complete if the system volume is being converted to Dynamic. After the disks are converted, perform the following steps to set up a Mirrored volume or RAID 1 of the system volume:

  1. Click Start, All Programs, Administrative Tools, Computer Management.

  2. In the left pane, if it is not already expanded, double-click Computer Management (local).

  3. Click the plus sign next to Storage, and select Disk Management.

  4. In the right pane, right-click the system volume and choose Add Mirror.

  5. Choose the disk on which to create the mirror for the system volume and click Add Mirror.

  6. The volumes on each disk start a synchronization process that might take a few minutes or longer, depending on the size of the system volume and the types of disks being used. When the mirrored volume's status changes from Re-synching to Healthy, select File, Exit in the Computer Management console to close the window.

Using the Diskpart Command-Line Utility

Diskpart.exe is a flexible command-line disk management utility that performs most of the functions available to it with the Disk Management console. Using diskpart.exe, both basic volumes and dynamic volumes can be extended whereas the Disk Management can only extend dynamic volumes. The real value of using Diskpart.exe is that it can be run with a script to automate volume management. This is particularly useful when automating server builds across several servers that have the same characteristics. For more information on automatic server installations, refer to Chapter 11, "Implementing Windows Server 2003."

Extend a Basic Volume Using Diskpart.Exe

If you want to extend a basic volume using diskpart.exe, the unallocated disk space must be on the same disk as the original volume and must be contiguous with the volume you are extending. Otherwise, the command will fail.

The syntax for Diskpart.exe is as follows:

Diskpart.exe /s script

The script referenced by the utility is a text file that will include the specific instructions necessary for the desired function. For example, to extend a volume using unallocated space on the same disk, the associated script file would look like this:

Select Volume 2
Extend
Exit
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