Friday, 6 November 2009

RAID part 3 RAID Level 1.

RAID Level 1

RAID level 1 is known as disk mirroring. Disk mirroring uses two or more hard drives and duplicates the data from one drive to the others. The fact that RAID 1 does store a second copy of the data on another member of the volume means that this solution does offer fault tolerance. Fault tolerance is the concept that if one part of the solution fails, the other guy will pick up the workload and the solution will continue to function. If one of the disks in the mirror fails, you can replace the failed disk by breaking the mirror, adding a new functioning disk, and then rebuilding the mirror from the existing disk that did not fail. Once you have reestablished the mirror, you have your fault tolerance back.

The figure below displays the concept of a mirror volume. When a user saves data to a mirrored volume, the data is written to all disks that make up the volume.

RAID level 1 (Mirror) concept.

Creating a Mirrored Volume in Windows Server

In this step-by-step you will create a mirrored volume on a Windows server using two of the dynamic disks created in the preceding walkthrough. Remember that a mirrored volume stores all the data on both members (disks) in the volume. To create a mirrored volume, follow these steps:

1. Right-click My Computer and choose Manage.

2. Right-click an area of unallocated space on disk 1 and choose Create Volume.

3. The Create Volume Wizard appears. Click Next.

4. Choose the volume type of Mirrored Volume, which is the volume type you wish to create, and choose Next.

5. Choose two or more disks  as a selected disk for the mirrored volume and type 200 Mb as the total amount of space used on each disk. Also notice that the total space used by the volume is 200Mb as well. Although there is 200MB per disk, you can store only 200Mb the other 200MB is to store a copy of the data in case of disaster.

6. Click Next.

7. Assign drive Y as the drive letter and choose Next.

8. Choose Next to format for NTFS and other settings.

9. Choose Finish. The mirrored volume is created. Notice that the legend in disk management displays the color codes for each volume type.

RAID 1 using hardware controllers:
RAID 1 is known as disk mirroring whereby the data is duplicated across two different disks but using only one disk controller. When using two disk controllers, one with each a hard disk connected to it, we term the RAID 1 solution disk duplexing rather than disk mirroring.

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