Maybe it's just a matter of style, but I would write that as either:

for ( `diskpart rescan` )
{
    . . .
}
[download]

or

open FH, "diskpart rescan |" or die "open diskpart|: $!"
while (<FH>)
{
    . . .
}
close FH;
[download]

And I think there may be a chomp or two missing in there...