Microsoft Exchange 2000 Operations Guide — Version 1.086
However, this does not mean that an Active Directory failure makes Exchange 2000
completely unusable. You should be able to recover an Exchange Organization, pro-
vided you have access to information about the Exchange configuration, including the
Exchange storage group and store names for each server, plus a key item, known as the
legacyExchangeDN attribute for each administrative group. Although this attribute is
designed to allow servers running Exchange 5.5 and Exchange 2000 to communicate with
one another, the attribute is used by all servers running Exchange, and the legacyExchangeDN
of the server must match that of its administrative group. It is worth noting however that
this procedure across an enterprise will cost a huge amount of time, pain and money and
should be avoided if at all possible.

Alternate Server Recovery

You may wish to perform alternate server recovery for a number of reasons. One of the
most common is that you need to perform some sort of database maintenance and you
want to check that the maintenance will not cause any problems with the database (you
should note however, that unless the hardware of the alternate server is identical, you
cannot guarantee that the same results will occur in the live environment). Another reason
for alternate server recovery is to recover a mailbox that has expired from the Exchange
Server.
Alternate server recovery is like rebuilding Exchange when you have lost Active Directory
except on a much smaller scale. If you are recovering Exchange stores onto another server
while the original server exists, the second server must be in a separate Windows 2000
forest. You will need to know the storage group and database names on the original server
and the legacyExchangeDN of the administrative group the server belongs to.
You may end up performing alternate server recovery quite regularly. For example, you
may undergo this process and then perform offline defragmentation of the database. If the
offline defragmentation produces significant reduction in the database size, you could then
take the production server offline to defragment it (depending on the terms of your SLA).
If alternate server recovery is a regular part of your operations routine (and it probably
should be, as discussed in the next section), you should have a separate Windows 2000
forest set up permanently. This forest would contain administrative groups with all the
correct legacyExchangeDNs already set up, preventing you from having to recreate it each
time you did the alternate server restore.
Recovery Testing
The key to reducing downtime during a restore procedure is to assume that system failure
will happen and that you are fully prepared for it when it does. This involves having
hardware, software, and backup sets available. It also involves having staff trained in
restore procedures available at all times.