disk failure. In other words, RAID-0 is not fault tolerant; a single disk event will cause the entire striped set to be lost, and it will have to be re-created through some type of recovery process, such as a tape backup.
RAID-1 (Disk Mirroring) Disk mirroring is two logical volumes on two separate identical disks created as a duplicate disk set. Data is written on two disks at the same time; that way, in the event of a disk failure, data integrity is maintained and available. Although this fault tolerance gives administrators data redundancy, it comes with a price because it diminishes the amount of available storage space by half. For example, if an administrator wants to create a 300GB mirrored set, they would have to install two 300GB hard drives into the server, thus doubling the cost for the same available space.
RAID-5 Volume (Disk Striping with Parity) With a RAID-5 volume, you have the ability to use a minimum of three disks and a maximum of 32 disks. RAID-5 volumes allow data to be striped across all of the disks with an additional block of error-correction called parity. Parity is used to reconstruct the data in the event of a disk failure. RAID-5 has slower write performance than the other RAID types because the OS must calculate the parity information for each stripe that is written, but the read performance is equivalent to a stripe set, RAID-0, because the parity information is not read. Like RAID-1, RAID-5 comes with additional cost considerations. For every RAID-5 set, roughly an entire hard disk is consumed for storing the parity information. For example, a minimum RAID-5 set requires three hard disks, and if those disks are 300GB each, approximately 600GB of disk space is available to the OS and 300GB is consumed by parity information, which equates to 33.3 percent of the available space. Similarly, in a five-disk RAID-5 set of 300GB disks, approximately 1,200GB of disk space is available to the OS, which means that 20 percent of the total available space is consumed by the parity information. The words roughly and approximately are used when calculating disk space because a 300GB disk will really be only about 279GB of space. This is because vendors define a gigabyte as 1 billion bytes, but the OS defines it as 230 (1,073,741,824) bytes. Also, remember that file systems and volume managers have overhead as well.
Table 1.4 breaks down the various aspects of the supported RAID types in Window Server 2012 R2.
TABLE 1.4 Supported RAID-level properties in Windows Server 2012 R2
Creating RAID Sets
Now that you understand the concepts of RAID and how to use it, you can look at the creation of RAID sets in Windows Server 2012 R2. The process of creating a RAID set is the same as the process for creating a simple or spanned volume set, except for the minimum disk requirements associated with each RAID type.
Creating a mirrored volume set is basically the same as creating a volume set, as shown in Exercise 1.6, except that you will select New Mirrored Volume. It is after the disk select wizard appears that you’ll begin to see the difference. Since a new mirrored volume is being created, the volume requires two disks.
During the disk select process, if only one disk is selected, the Next button will be unavailable because the disk minimum has not been met. Refer to Figure 1.3 to view the Select Disks page of the New Mirrored Volume Wizard during the creation of a new mirrored volume, and notice that the Next button is not available.
FIGURE 1.3 Select Disks page of the New Mirrored Volume Wizard
To complete the process, you must select a second disk by highlighting the appropriate disk and adding it to the volume set. Once the second disk has been added, the Add button becomes unavailable, and the Next button is available to complete the mirrored volume set creation (see Figure 1.4).
FIGURE 1.4 Adding the second disk to complete a mirrored volume set
After you click Next, the creation of the mirrored volume set is again just like the rest of the steps in Exercise 1.5. A drive letter will have to be assigned, and the volume will need to be formatted. The new mirrored volume set will appear in Disk Management. In Figure 1.5, notice that the capacity of the volume equals one disk even though two disks have been selected.
FIGURE 1.5 Newly created mirrored volume set
To create a RAID-5 volume set, you use the same process that you use to create a mirrored volume set. The only difference is that a RAID-5 volume set requires that a minimum of three disks be selected to complete the volume creation. The process is simple: Select New RAID-5 Volume, select the three disks that will be used in the volume set, assign a drive letter, and format the volume. Figure 1.6 shows a newly created RAID-5 volume set in Disk Management.
FIGURE 1.6 Newly created RAID-5 volume set
Mount Points
With the ever-increasing demands of storage, mount points are used to surpass the limitation of 26 drive letters and to join two volumes into a folder on a separate physical disk drive. A mount point allows you to configure a volume to be accessed from a folder on another existing disk.
Through Disk Management, a mount point folder can be assigned to a drive instead of using a drive letter, and it can be used on basic or dynamic volumes that are formatted with NTFS. However, mount point folders can be created only on empty folders within a volume. Additionally, mount point folder paths cannot be modified; they can be removed only once they have been created. Exercise 1.6 shows the steps to create a mount point.
EXERCISE 1.6: Creating Mount Points
1. Open Server Manager.
2. Click and then expand Storage.
3. Select Disk Management.
4. Right-click the volume where the mount point folder will be assigned, and select Change Drive Letter And Paths.
5. Click Add.
6. Either type the path to an empty folder on an NTFS volume or click Browse to select or make a new folder for the mount point.
When you explore the drive, you’ll see the new folder created. Notice that the icon indicates that it is a mount point.
Microsoft MPIO
Multipath I/O (MPIO) is associated with high availability because a computer will be able to use a solution with redundant physical paths connected to a storage device. Thus, if one path fails, an application will continue to run because it can access the data across the other path.
The MPIO software provides the functionality needed for the computer to take advantage of the redundant storage paths. MPIO solutions can also load-balance data traffic across both paths to the storage device, virtually eliminating bandwidth
