Backing Up a DC
The first step toward backing up a DC is to install Windows Server Backup on your
Server 2008 system. On a full server installation,
using Server Manager’s Add Features
Wizard is the easiest approach. On a Server
Core system, execute the command
ocsetup WindowsServerBackup
Before you perform any backups, you
need to configure the Optimize Backup
Performance settings for Windows Server
Backup. You can find these settings in the
Windows Server Backup menu’s task pane
or by right-clicking the Windows Server
Backup node under Storage in the Server
Manager tree. By default, Windows Server
Backup always performs a full backup, but
as Figure 2 shows, you can configure it to
perform incremental backups. Unfortunately,
Server Core offers no command-line
option to help you configure the settings.
Microsoft recommends connecting to the
Server Core box from a full server running
Windows Server Backup and configuring
the settings remotely.
The Optimize Backup Performance
settings let you specify whether Windows
Server Backup should keep or erase the VSS
snapshots that it automatically creates on
the source disk during each backup cycle.
When you choose incremental backups, you
choose to keep the snapshots on the disk;
when you choose full backup, the snapshots are erased after
the backup is finished.
Keeping the snapshots
lets the system automatically
track changes on
the source disk at runtime.
However, tracking
changes requires VSS to
copy the original block
to the shadow copy area
before overwriting the
source block. That procedure
initiates extra
disk activity and requires
additional space on the
source disk. On servers
with write-intensive
applications, keeping the
shadow copies can slow
disk performance.
Which option should
you choose for your DCs?
Incremental backups are
better for two reasons.
First, DCs are much more often read from
rather than written to, so they tend not to
be write intensive and don’t take much of
a performance hit from the VSS activity.
Second, you can use the shadow copies
for other AD recovery options. For each
of your hard disks, you can configure the
amount of space devoted to snapshots by
using the Microsoft Management Console
Disk Management snap-in or the vssadmin
.exe command-line tool, both of which are
installed with the OS.
On a full-server system, you can configure
a backup with a few simple choices in
the Windows Server Backup UI. On Windows
Server Backup’s Action menu, click
Backup once to launch the Backup Once
Wizard and let it guide you through the
configuration process. When you reach the
Select backup items page, make sure that
the Enable system recovery check box is
selected to ensure recovery of the AD database.
The Enable system recovery option
backs up all volumes that contain systemstate
data. Note that you can also schedule
a backup; however, this option requires
a dedicated local disk that’s used only by
Windows Server Backup.
The best way to deploy DCs, however, is
on a Server Core system, as it is more secure
by default and thus reduces the attack surface
on your DCs. But of course, a Server Core deployment means that you have to do
most administration through the command
line. Here’s how to perform a backup from
the command line:
1. To back up the full system, including
all critical volumes (i.e., those that contain
system data such as the AD database),
thus allowing bare-metal recovery, run the
command
WBADMIN Start Backup –backupTarget:D:
-allCritical
replacing D: with the target drive on which
you’ll store the backup. If the target is a
network location, enter the Universal Naming
Convention path to the share
(e.g., \\Server2.corp.net\BackupData).
2. To back up only the system state, use
the command
WBADMIN Start SystemStateBackup
–backupTarget:C:
Note that this command doesn’t require
the -allCritical option; the Start System-
StateBackup command always backs up all
system data.
With either command, the result is a folder
on the target named WindowsImageBackup.
The folder contains a subfolder with the
server’s short name (“W2K8Full04” in Figure
3). The actual backup data is stored in the
server folder, primarily in a VHD file that
contains all the blocks of data. Some XML
files hold registry and other settings. You
can copy the whole WindowsImageBackup
folder to a different location (on the network
or on disk), but you must keep the same
folder structure to allow the recovery process
to find the backup data.
Unless you’re using the DC for many
other functions (which is most likely for
small-to-midsized businesses) and have no
opportunity to back up the full system to a
local drive, there isn’t much point in creating
just a system-state backup for DCs. A full system
backup of a Server 2008 DC that doesn’t
host a plethora of other services (which is
the optimal case for writeable DCs) typically
isn’t much larger than a system-state backup
of the same machine. More important, with
a full system backup you can perform incremental
backups, which you can’t when using
the system-state backup option. Incremental
backup saves considerable time and disk
space if you want to keep multiple backup
versions on your target disk. Also, you can
use full-system-backup files to perform a
system-state recovery.
Performing a Complete DC Recovery
Recovering a Server 2008 DC from scratch
with Windows Server Backup involves a
few more steps than does performing the
backup. But compared to the process for
earlier Windows OSs, which used Ntbackup
to perform full system recoveries, the new
process is fairly simple: It doesn’t require
you to first reinstall the OS, but simply
applies the image of the system volume(s)
stored in the backup’s VHD file(s).
1. Boot the server from Server 2008
installation media. Doing so boots the
server into the same Windows Preinstallation
Environment session that you use to
deploy a new Server 2008 instance.
2. At the Install Windows screen, choose Repair your computer at the bottom left.
This option starts the Windows Recovery
Environment (Windows RE), which lets you
perform various repair and recovery tasks on the server. Windows RE tries to determine
which OS is installed on the server and
requires access to the local disks at this time;
if necessary, you can load drivers from CD,
DVD, USB, or the floppy drive.
3. After Windows RE finds and selects
your OS, click Windows Complete PC
Restore to do a full system recovery. The
Windows Server Backup restore procedure
searches the local, USB, and DVD drives
for the disk-based backup media to use as
the source for the system recovery. You can
also manually connect to a network share
to recover the system from a backup stored
on a remote machine.
4. Choose the backup source you want
to use for the actual recovery operation.
A complete recovery wipes all data from
the target disk and performs a block-level
restore. If your system has multiple volumes,
you can choose to recover specific
volumes; only those you choose to recover
will be erased during the recovery procedure.
You’ll be prompted to acknowledge
the erasure of all data on the target disk
before the recovery proceeds.
5. After completing the restore, the system
will automatically reboot the DC and
bring it back online. The DC will then synchronize
with AD to replicate all changes
that were made since the backup was performed.
Combining a full system recovery of a
Server 2008 DC with an authoritative restore
of objects (e.g., to recover an accidentally
deleted object) requires special precautions.
You need to ensure that the server boots into
DSRM (press F8 during the boot sequence
to choose DSRM) immediately after the
system recovery is complete (i.e., before
replicating with other DCs). Server 2008
still requires DSRM to allow access to the
AD database for performing authoritative
restores using the Ntdsutil tool. This process
hasn’t changed from earlier OS versions.
Performing a System-State
Recovery
If you need to recover only AD, you can
restore just the DC’s system state. However,
a system-state restore requires a fully
operational OS. Also, because the Windows
Server Backup UI doesn’t support a systemstate
restore, you need to use the Wbadmin
command-line tool. A system-state recovery of a Server 2008 DC is a bit
tedious because you must use the
command line, but the process
is similar to that of restoring the
system state of an earlier version
of Windows.
1. Boot the DC into DSRM
by pressing F8 during the boot
sequence and use the recovery
password to log on as Administrator.
If necessary, you can
recover the system state to a
brand-new, similarly configured
Server 2008 server on which the
Windows Server Backup feature
is installed.
2. Open a command prompt
and locate available backup versions
via Wbadmin by using the command
wbadmin get versions
-backupTarget:drive_or_share
machine:servername
where drive_or_share is the path to the
backup target and servername is the name
of the machine being restored. The output
will resemble that in Figure 4.
3. From the output, identify the backup
version to use for the system-state recovery.
You can recover the system state from
any backup that lists System State in the
Can Recover line. Copy the version identifier
(e.g., 01/27/2008-15:18) for use in the
next step.
4. Start a system-state recovery of the
desired backup version using the following
Wbadmin command:
wbadmin Start SystemStateRecovery
-version:versionID
backupTarget:drive_or_share
machine:servername
where versionID is the version identifier
from the Get Versions output. When
prompted, confirm the recovery. Wbadmin
will mount the backup’s VHD file and copy
the required files to the source drive. Be
prepared: A system-state restore can take
considerably longer than a full-volume
recovery, which is block-based.
5. After recovery, the server will want to
reboot. If you want to perform an authoritative
restore of AD objects, don’t reboot
until you’ve run Ntdsutil with the appropriate
options.
6. Reboot the system to replace all files that were in use during recovery. Rebooting
takes time, and the server might have to
reboot more than once to replace specific
files and complete the system-state recovery,
but rebooting is an important part of
the recovery process. Successful systemstate
recovery is confirmed by a command
prompt at the first logon after rebooting.
Forest Recovery Considerations
With this background information, you
should be well prepared to plan your own
DC backup and recovery. This information
might even affect how you plan to set
up the volumes used on a DC for data and
for backup, because you’ll need a separate
target volume for your backups when using
the full-system backup method. I recommend
performing a volume-based fullsystem
backup over a system-state backup
if your DC configuration allows it—a fullsystem
backup is more efficient and lets
you perform fast incremental backups. Both
methods let you restore just the system state
(which is required to restore the AD database
on a DC). However, a volume-based
system recovery outperforms a file-based
system-state recovery.
Forest recovery continues to be a special
challenge, which I don’t have room to go
into here. But as long as you back up your
DCs regularly and have at least two DCs per
domain in your forest, you’re prepared to
perform a forest recovery as well.
A major benefit of Server 2008 is that ideally
you’ll deploy writable DCs only within
your well-connected hub sites and use
RODCs in all locations outside of your hub
data centers that contain DCs. The benefits of using RODCs include a smaller attack
surface and improved security for your
overall IT infrastructure. However, RODCs
also provide benefits from a forest-recovery
perspective because they don’t require the
same attention as writeable DCs during
recovery. RODCs can’t replicate data to the
hub, and that makes for a much smoother
and faster forest recovery. RODCs help you
concentrate on your hubs and recovering
your DCs without worrying about interference
from remote DCs. After the hubs are
online and working, you can tackle the
RODCs at the remote sites.
Taming the AD Backup Beast
AD backup and recovery is still a complex
process in Server 2008. You have powerful
new options to help you with this task, but
you need to learn how to use them correctly.
In an upcoming article, I’ll explain how VSS
snapshots provide a feasible way to recover
attribute data from AD, letting you implement
a real online recovery of objects that
you might have accidentally deleted. I’ll also
show you some new options in Server 2008
that help prevent accidental deletion of AD
data.