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Understanding RAID

RAID is a collection of strategies designed to provide fault tolerance for files stored on hard drives (it can be used to protect boot and system files as well). In general, using RAID means that you are placing data on more than one disk. If a disk in the RAID set goes down, you still have access to your data because you either have a complete copy of that data (on the other disk in the RAID 1 mirror set) or can read the data on the failed disk from the data and parity information (discussed later in this hour when we look at RAID 5) on the remaining disks in the array.

In the simplest terms, RAID enables you to combine volumes on more than one drive into a volume set (or array) that functions as a single logical drive.

There are at least 13 different levels of RAID and most of these RAID implementations require drive controllers that support hardware RAID configurations. As already mentioned, Windows Server 2008 allows you to implement software implementations of RAID. Windows Server supports software versions of RAID 0, 1, and 5. Table 6.1 provides definitions of these three software RAID possibilities.

Table 6.1. Windows 2008 Server Software RAID Levels
Level Name Description
0 Striping without parity Data is written across the disks in the array. RAID 0 is not a fault-tolerance method; it’s actually used to speed disk access.
1 Mirroring Two drives (such as partitions or volumes) are mirrored so that each disk in the array is an exact copy of the other disk.
5 Disk striping with distributed parity Data is written across a stripe set of multiple disks, with the parity information distributed across the disk array.

By the Way

RAID can be either hardware or software supported. A number of RAID controllers are available for network servers. We discuss the software RAID levels embraced by Windows Server 2008. RAID configurations can even be expanded beyond a single server. Windows Server 2008 also supports server clustering. This enables you to tie a number of servers into a cluster, producing extremely powerful processing and a high storage capacity environment.

Let’s take a look at implementing the software RAID levels provided by Windows Server 2008 and how they allow you to build fault tolerance into your server implementations.

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