How to Create a Spanned Volume

A spanned volume uses the free space on more than one physical hard disk to create a bigger volume. The portions of disk used to create the volume do not need to be the same size and can actually include more than one free space on a disk. A spanned volume provides no additional speed benefits and increases the risk of catastrophic failure leading to data loss. The failure of any disk involved in the spanned volume will make the entire volume unavailable.

Note To achieve a speed benefit with multiple disks, you must use striping, such as that provided by RAID 1 or RAID 5. With striping, every file on a volume is evenly distributed between multiple physical disks. With striping, files can be read from or written to multiple disks simultaneously, increasing throughput. Spanning simply appends one disk to the next, so any given file is probably stored only on a single disk. The best way to add striping is to use a computer or add-on card that supports hardware RAID.

If you still want to create a spanned volume, follow these steps:

1. Open the Disk Management snap-in.
2. Right-click a free-space segment that you want to include in the spanned volume and then select New Spanned Volume from the shortcut menu. The New Spanned Volume Wizard appears.
3. Click Next. On the Select Disks page, select from the available disks and then click Add to add the disks to the spanned volume. Select each disk in the Selected column and set the amount of space to use on that disk for the spanned volume. Click Next.
4. On the Assign Drive Letter Or Path page, the default is to assign the next available drive letter to the new volume. You can also mount the volume on an empty NTFS folder on an existing volume. Click Next.
5. On the Format Volume page, choose the formatting options for the new volume. Windows Vista and Windows 7 support only NTFS formatting from the Disk Management snap-in. To format with FAT or FAT32, you need to use the command line. Click Next.
6. Click Finish on the summary page to create the volume.

Creating a spanned volume using DiskPart is a somewhat more complicated process than creating a simple volume. You can't just create the spanned volume in one step; you need to first make sure that the disks to be used are converted to dynamic. Then you create a simple volume on the first disk of the spanned volume, extend the volume to the second disk, and then add any additional disks involved in the span. Finally, you must assign the volume to a drive letter or mount point.