Creating and Managing Windows Server 2008 Striped (RAID 0) Volumes
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The focus of this chapter of Windows Server 2008 Essentials is the configuration of striped or RAID 0 volumes on a Windows Server 2008 system. It is assumed in this chapter that the reader has a basic understanding of the difference between basic and dynamic disks within the context of Windows Server 2008. For information on this subject the chapter entitled Creating and Managing Simple and Spanned Volumes on Windows Server 2008 is recommended.
An Overview of Striped (RAID 0) Volumes
Striped (otherwise known as RAID 0) volumes consist of a stripe set comprised of two or more similar sized disk drives (up to a total of 32 drives). When data is written to a striped volume the data is divided into a number of stripes equal to the number of disks in the striped set and a stripe is written to each disk. Similarly, when data is read from the volume, each stripe of data is read from the disks in the striped set before being combined into its original form.
The primary purpose of striped volumes is improved disk I/O performance. By dividing the read and write process over multiple disk drives any bottlenecks associated with using a single disk drive are avoided. The downside of disk striping is that the loss of a single disk in the stripe set results in the loss of all the data since the data on the remaining drives in the stripe set is of little use without the missing stripes residing on the failed drive.
Creating a Striped (RAID 0) Volume using Disk Management
In this section a striped volume will be created using two similarly sized disk drives connected to a Windows Server 2008 system (note that if the disks are of different sizes Windows will base the available volume size on the smallest disk drive in the striped set).
Begin the process by invoking the Disk Management snap-in. This can be achieved by typing compmgmt.msc at a command prompt window or Run dialog and selecting Storage -> Disk Management. The system used in this example contains three disks numbered 0, 1 and 2 respectively. Disk 0 is the system disk and disks 1 and 2 will be used to create a striped set.
Within the Disk Management tool right click on the unallocated space in the graphical view of the first disk to be used in the stripe set and select Create New Striped Volume... to invoke the New Striped Volume wizard. Click Next on the welcome screen to proceed to the disk selection screen. As mentioned previously, a striped set can be comprised of anywhere from 2 to 32 disk drives. For the purposes of this example the set will consist of two disks. Initially, the wizard only lists the currently selected disk in the Selected column. In order to proceed, at least one more disk is required. To add disks to the striped, select a suitable disk from the available disks in the right hand column and click on Add to add it to the selected disks list: <google>WIN28BOX</google>
With the necessary disks selected click Next to proceed and assign a drive letter or mount point for the volume. The Next button will then proceed to the Format Volume screen where the file system type and compression options may be selected. To view the summary screen, press the Next button. Assuming the summary is acceptable the Finish button will format the volumes and create the striped volume ready for use.
Creating a Striped (RAID 0) Volume from the Command Prompt
Windows Server 2008 Striped (RAID 0) volumes may also be created from the command prompt using the diskpart tool. This may be launched either from a command prompt window, or from the Run dialog simply by entering diskpart at the prompt. Once invoked the DISKPART> prompt will displayed, ready to receive commands.
The first step in creating a striped volume using diskpart is to identify the disks to be used in the striped set. This can be achieved using the list disk command:
DISKPART> list disk Disk ### Status Size Free Dyn Gpt -------- ---------- ------- ------- --- --- Disk 0 Online 30 GB 0 B Disk 1 Online 8 GB 8189 MB Disk 2 Online 8 GB 8189 MB
For the purposes of this tutorial we will be creating a striped volume based on a stripe set consisting of disks 1 and 2. The striped volume is created using the create volume command combined with the stripe and disk= directives. In the case of the disk= directive a comma separated list of disk numbers to be used in the striped set must be provided. The size of the volume may also be specified using the size= directive. Omission of the size= option will cause diskpart to create volume such that it is the size of the smallest disk in the striped set. For example, to create a striped volume comprising of disks 1 and 2:
DISKPART> create volume stripe disk=1,2 DiskPart successfully created the volume.
Having created the striped volume, the list volume command may be used to verify the new configuration:
DISKPART> list volume Volume ### Ltr Label Fs Type Size Status Info ---------- --- ----------- ----- ---------- ------- --------- -------- * Volume 0 RAW Stripe 16 GB Healthy Volume 1 D DVD-ROM 0 B No Media Volume 2 C NTFS Partition 30 GB Healthy System
As shown above the new volume is listed as volume 0 and shown as Stripe. The volume is also listed as RAW because it has not yet been formatted with a file system. This, too, can be achieved within the diskpart tool:
DISKPART> select volume 0 DISKPART> format fs=ntfs label="My Striped Vol" 100 percent completed DiskPart successfully formatted the volume.
Once formatted, the last task is to assign either a drive letter or mount point to the volume by which it will be accessed:
To assign a drive letter:
DISKPART> assign letter=E: DiskPart successfully assigned the drive letter or mount point.
To assign a mount point:
DISKPART> assign mount=\bigvol DiskPart successfully assigned the drive letter or mount point.
Once assigned a drive letter or mount point, the new striped volume is ready for use.
Recovering a Striped Volume
When a disk in a striped set fails or goes off-line the volume will be listed as either Missing, Offline, Failed or Unreadable. If the disk is offline or missing the first thing to check is that all drives in the striped set are powered up and that the connectors are firmly in place. If a disk can be brought back on line the next step is to instruct Windows to rescan the disks so that striped volume can be brought back online. Do this by selecting Rescan disks from the Action menu. If the disk is listed as failed, unreadable or shows errors then the disk may have physical errors which suggest the disk needs to replaced and the data on the striped volume restored from the most recent back up.
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