Been hunting around the net after the tip from KovBal about dynamic disks - and came across this thread.
Basically, RAID using external USB hard drives doesn't look too achievable.
One quote here.
Using USB as the transfer technology
you're only going to achieve a
30-Megabyte or less transfer rate. You
seem to be going to a lot of effort
for a marginal result. For external
use, eSATA is a much better choice for
Maybe I don't understand the intent,
but having 3 USB external drives
working as a single "Dynamic" volume
is almost certainly going to saturate
the Hubs/Controller they are on.
And another quote here.
The overhead of software RAID will
probably cause problems on USB drives.
Even if you get it working I think it
will probably be flaky and error
prone. You can buy USB enclosures that
you can install multiple drives in.
These enclosures use an embedded Linux
so that you can then setup a RAID
array. This way the RAID calculations
and read/writes are all done outside
of Windows. The interface can be USB,
SCSI, eSATA, LAN, whatever, it makes
no difference. Software RAID is a
compromise at best. I don't believe
RAID 5 is supported in Vista in any
case. I would look for a different way
to achieve your goal.