| Hard disks are typically static configurations where the only method to add a new drive is to create a new partition. In many cases, it is preferable to extend a partition to include the space in a new hard drive. Dynamic disks allow the user to create a special disk partition which can be extended as new hard drives are installed - i.e. two 120 GB hard disks can act as a single 240 GB partition. When the 240 GB partition is nearly full, the user can install another 120 GB disk and extend the partition to 360 GB without needing to reformat the set of drives - you just install the new drive, and select extend dynamic disk, and like magic, it is done.
Before experimenting with new technology it is generally sound advice to backup your data.
A partition can be made into a dynamic volume by right clicking on the disk from within Computer Management. Under Windows 2000 Professional, a disk can be setup as spanned, striped, or mirrored. Spanned means that the disk can be extended with new hard drives. Striped means that the data is written on multiple drives at once so that performance can be improved linearly relative to the number of hard drives in the striped configuration. Mirrored means that the data is copied to the other drive as it is written.
In high performance applications such as video editing and analysis, hard disk speed can be a limiting factor. In this case a striped set of disks can overcome the performance bottleneck.
If your data is very important, then mirroring the data on another disk is clearly the best option. If one of the drives dies, the other will have all of the information intact.
In Windows 2000 Advanced Server, there is also the option to make the set of disks RAID Level 5, which means that an additional disk is necessary for keeping track of data parity. i.e. in the case of the two 120 GB drives, an additional smaller disk (say 40 GB) would be used to keep track of the parity information over the disks so that if one of the disks died, a new blank disk could be inserted into the configuration and the data could be recovered.
Note that when converting an existing non-dynamic disk to a dynamic disk, it is usually necessary to reformat the disk.
If one of the disks in a spanned dynamic disk setup dies, then all of the information in the spanned setup is lost.