The reason appears here:
Dynamic disks are not supported for USB devices. The help and MSDN
say this. You can fake around it in WinXP by attaching a drive to a
SATA or IDE port, changing it to dynamic, then putting the drive in a
USB enclosure. It appears they decided to enforce this restriction
That's a drag, as it will make it difficult to mount a drive
from a different machine on a USB chain, which you sometimes need to
do to make repairs.
Microsoft is now enforcing the no-USB policy for Dynamic Disks.
If it is a single disk dynamic disk (not spanned or striped to another disk or set of disks), you MAY be able to convert it to a Basic Disk.
To change a dynamic disk back to a basic disk:
- Back up all the data on all the volumes on the disk you want to convert to a basic disk.
- Log on as Administrator or as a member of the Administrators group.
- Click Start, and then click Control Panel.
- Click Performance and Maintenance, click Administrative Tools, and then double-click Computer Management.
- In the left pane, click Disk Management.
- Right-click a volume on the dynamic disk that you want to change to a basic disk, and then click Delete Volume.
- Click Yes when you are prompted to delete the volume.
- Repeat steps 4 and 5 for each volume on the dynamic disk.
- After you have deleted all the volumes on the dynamic disk, right-click the dynamic disk that you want to change to a basic disk,
and then click Convert to Basic Disk.
NOTE: You must right-click the gray area that contains the disk title on the left side of the Details pane. For example, right-click