Simple volume

A dynamic simple volume consists of a single contiguous region (or subdisk) on a single physical disk. Dynamic simple volumes can be extended or mirrored. When you extend a simple volume to a noncontiguous region within the same disk or onto additional disks, it becomes a spanned volume.

Spanned volume

A dynamic spanned volume consists of two or more subdisks (single contiguous regions) on one or more disks. With a spanned dynamic volume, you can combine sections of unallocated space from multiple dynamic disks into one large volume. The areas of unallocated space used to create spanned volumes can be different sizes. Spanned volumes are organized sequentially - that is, Storage Foundation sequentially allocates space on each disk until that disk is full and then continues with the next disk until the volume size is reached. Up to 256 disks can be included in a spanned volume.

You can expand the existing spanned volumes by the amount of unallocated space on all the disks in the dynamic disk group. However, after a spanned volume is extended, no portion of it can be deleted without deleting the entire spanned volume.

The advantage of a spanned volume is that it lets you create a large volume consisting of smaller pieces of disk space from several disks, thereby making more efficient use of the disk space than would be possible if you had to limit the volume to a single disk. The disadvantage of a spanned volume is that it is not fault tolerant. If one of the disks containing a spanned volume fails, the entire volume fails. However, a spanned volume can be mirrored.