Fail Over DC/DHCP Server - Possible?

Hi all

The History

A couple of times we have had a drive failure on our HP Proliant ML370 G6
Win Server 2008 R2.
The drive, one half of a mirror on the OS, has failed and basically caused
the server to freeze.
According to HP tech support, it is necessary for the failed drive to be
physically removed for the hot spare to rebuild the mirror and the server to
come back into service (it actually comes back on line once the array
rebuild has started).
I thought that the hot spare substitution would be transparent and not
require physical intervention....

The Question

Is it possible to have another server prepared/equipped to perform the roles
of DC and DHCP in the event that the primary box fails?
The primary box in question covers DC, DHCP and file/print duties. But if
another box could cover the DC and DHCP duties as an automatic fail-over,
then at least we could simply shut down the failed primary box and still
logon and access emails on our Exchange box.


Thanks

Phil