The acronym RAID stands for Redundant Array of Independent (or Inexpensive) Disks—it is a series of separate disks configured to work together as a single drive with a single drive letter. You have already seen three of the most common types of RAID arrays in Table 3-3 : RAID 0 (disk striping), RAID 1 (mirroring), and RAID-5 (disk striping with parity). Other versions of RAID also exist but are generally unused; you are unlikely to see these referenced on the 70-410 exam.
ptg14504686 Creating a RAID 0 Volume
A RAID 0 (striped) volume contains space on 2–32 separate hard disks. Data is writ- ten in 64-KB blocks ( stripes ) to each disk in the volume, in turn. A striped volume offers considerable improvement in read/write efficiency because the read/write heads on each disk are working together during each I/O operation. A striped vol- ume offers a maximum amount of space equal to the size of the smallest disk multi- plied by the number of disks in the volume. However, the striped volume does not offer fault tolerance; if any one disk is lost, the entire volume is lost. Note that the system or boot volume cannot be housed on a striped volume.
You can create a striped volume by using 2–32 separate hard disks in Disk Manage- ment. Use the following procedure:
1. In Disk Management, right-click any one disk to be made part of the striped volume, and select New Striped Volume .
2. The New Striped Volume Wizard starts and displays the Select Disks page shown in Figure 3-11 . The disk you initially selected appears under Selected. Select the disks you want to use from the Available column, and then click Add .
Figure 3-11 You need to select at least two disks to create a striped volume.
3. Disks you add appear in the Selected column. If you want to change the amount of space to be allocated, modify the value under Select the amount of space in MB . When done, click Next .
ptg14504686
4. From the Assign Drive Letter or Path page, accept the default, choose another drive letter, or select the option to mount the volume in an empty NTFS folder if desired. Then click Next .
5. Choose the desired options in the Format Volume page, and then click Next .
6. Review the information on the completion page, and then click Finish .
7. If any of the disks to be used in the volume are configured as basic disks, you receive the same message warning you that you will be unable to boot other operating systems, as shown previously in Figure 3-10 . To create your volume, you must click Yes and convert these disks to dynamic storage, as discussed earlier.
8. The volume is created and formatted, and appears in the Disk Management snap-in display, as shown in Figure 3-12 .
Figure 3-12 New striped volume.
NOTE While you can use different-sized drives, your stripe is created using the smallest drive. The remaining space on the larger drive will appear as unallocated free space.
ptg14504686 Creating a Spanned Volume
You can extend storage space on an existing volume to a new disk by creating a spanned volume. This is essentially a volume that spans two or more disks and enables you to add space without the need to specify a new drive letter. Note that the spanned volume is even less fault tolerant than a simple volume—if any one disk fails, all data is lost from all disks and must be restored from backup.
To create a spanned volume, right-click the desired volume and select Extend Volume . From the Extend Volume Wizard, select the available disk(s) and com- plete the steps in this wizard, as previously described and shown in Figure 3-4 . Creating a Mirrored Volume
A mirrored volume contains two disks, each of which is an identical copy of the other, thereby providing fault tolerance at the expense of requiring twice the amount of disk space. You can use a mirrored volume to provide fault tolerance for the system and boot volumes, as well as any data volumes.
Creating a mirrored volume is similar to that of creating a striped volume. Use the following procedure:
1. In Disk Management, right-click any one disk to be made a part of the mirrored volume and select New Mirrored Volume .
2. Steps displayed by the New Mirrored Volume Wizard are similar to those of the New Striped Volume Wizard and outlined in the previous procedure. When you have completed the procedure, the mirrored volume appears in the Disk Management display.
Creating a RAID-5 Volume
A RAID-5 volume is similar to a striped volume in that data is written in 64-KB stripes across all disks in the volume. However, this volume adds a parity stripe to one of the disks in the array, thereby providing fault tolerance. The parity stripe rotates from one disk to the next as each set of stripes is written. The RAID-5 vol- ume offers improved read performance because data is read from each disk at the WARNING Remember that RAID-0 is not fault tolerant. RAID-0 writes data in 64-KB blocks to each disk in the array sequentially, thereby improving read/write performance. However, if you lose any one of the disks in the array, all data is lost and you must restore the data from a backup after replacing the lost disk and re- creating the array.
ptg14504686 same time; however, write performance is lower because processor time is required
to calculate the parity stripes. You cannot house the system or boot volumes on a RAID-5 volume.
Creating a RAID-5 volume is also similar; remember that you must have at least three disks to create this type of volume. Select New RAID-5 Volume from the right-click options and follow the steps presented by the New RAID-5 Volume Wizard.
Managing and Troubleshooting RAID Volumes
Several things can go wrong with RAID volumes. Spanned and striped volumes are particularly vulnerable; as has already been mentioned, failure of any one disk in the volume renders the entire volume useless and data must be restored from a backup. If one disk in a mirrored volume fails, you can break the mirror and use the data on the other disk as a simple volume. If one disk in a RAID-5 volume fails, the system reconstructs the missing data from the parity information and the volume is still usable, but without fault tolerance and with reduced performance until the failed disk is replaced. If more than one disk in a RAID-5 volume fails, the volume has failed and must be restored from a backup after the disks have been replaced. Besides the volume statuses already described for partitions on basic disks and simple volumes, Disk Management can display the following messages with RAID volumes:
■ Resyncing : Indicates that a mirrored volume is being reinitialized. This status
is temporary and should change to Healthy within a few seconds.
■ Data Not Redundant or Failed Redundancy: For a mirrored or RAID-5
volume, this status usually means that half of a mirrored volume was imported, or that half is unavailable, or that only part of the underlying disks of a
RAID-5 volume were imported. You should import the missing disk(s) to re- create the volume. You can also break the mirror and retain the half that is functioning as a simple volume. If you have all but one of the underlying disks of a RAID-5 volume, you can re-create the RAID-5 volume by adding unallo- cated space of a different disk.
■ Stale Data: This status is shown when you import a disk that contains a mir- rored volume half, or a portion of a RAID-5 volume, with a status other than Healthy before it was moved. You can return the disk to the original PC and rescan the disk to fix the error.
NOTE For more information on how RAID-5 volumes function, refer to “RAID-5 Volumes” at http://technet.microsoft.com/en-us/library/cc938485.aspx .
ptg14504686