لطفا منتظر باشید ...
Restoring Data
This chapter describes the process of backing
up a network. Backup is only half the story, though; in order to do any good, a
backup must allow you to restore data. There
are two types of restore that you must consider: Partial restores In a partial restore, you need to
restore just a few noncritical files. For instance, a user might need a file
that was deleted last week, or you might need to recover an old set of log
files. Such a process is usually a fairly simple reversal of the process used
to create the backup. For instance, rather than use the --create option to tar , you use --extract and specify the filename or directory you want to restore. As noted
earlier, if you use a mounted filesystem and server-initiated backup, you must
ensure that the backup client's network server is configured for read-write
access from the backup server, which isn't a requirement for backups alone. Full restores The nightmare scenario for any backup procedure is a full restore, in which you must recover all the files on a disk, or at least all those
required to boot the computer. Such a situation can occur because a hard disk
failed or because of some software disaster, such as a computer that's been
accidentally wiped out by an errant command like rm -r / .WARNING
align=left border=0> One reason for doing a full restore is to
recover a system to a state prior to its invasion by a cracker. You must be
very cautious when doing such restores to both wipe out all the files the
invader left behind and to use a backup that predates the system's
compromise. Following such a restore, you must fix whatever problems existed
that allowed the computer to be cracked.
Full restores are difficult to handle because
you must find some way to get the restore onto a computer that has no working
software. One common approach to solving this problem is to prepare an
emergency restore system on a floppy disk, bootable CD-ROM, bootable Zip disk,
or the like. For network backup clients, this disk should include network
configuration tools and whatever network backup clients or servers you used to
create the backup in the first place.TIP
align=left border=0> Even if your network consists of a Linux
backup server and a large number of Windows 9 x /Me
backup clients, you can use a Linux-based emergency restore system. Such a
system can include Samba, and you can use it to run an SMB/CIFS server to
which the Linux backup server can restore files. After performing a full
restore, you may need to use DOS's FDISK to mark the boot
partition as bootable, and use the SYS program from the
version of Windows you've backed up to write a boot sector to the boot
partition. If you have Windows NT, 2000, or XP backup clients, the process
may be more complex, particularly if they use NTFS. In such a case,
installing the systems initially with a small boot partition you can back up
and restore with Linux's dd or a commercial tool like DriveImage can greatly simplify
restoration.
Sometimes, you may want to use a different
method for a full restore than you used for a backup. For instance, a
client-initiated Samba backup using a backup share might be more easily
restored by using either a client-initiated direct tar restore via rshd or a
server-initiated restore using either NFS or Samba.In some cases, and especially if you haven't
adequately planned an emergency restore procedure, you may have to reinstall
the base OS in order to restore normal backup client functionality. You can
then use this configuration to restore the rest of the data to the system, as
if it were a partial restore.AMANDA is unusual among the tools described
here in that it includes client-based restore tools. The most powerful of these
is amrecover , which in turn calls other tools such as amrestore . When
you type amrecover as root on the backup client to enter the recovery utility, the program
presents you with its own prompt at which you can type commands like setdate (to
set the date of a backup from which you want to recover), cd (to change
into a directory in the backup), add (to add a file to a restore set), and extract (to
restore files from a restore set). After you type extract , amrecover prompts you for the appropriate tapes to restore data.No matter what methods you use for
restoration, it's critical that you test them before they become necessary. Ideally,
you should set up a test system and try backing it up and performing both
partial and full restores on that test system. If your network hosts several
different OSs, repeat these tests with each of the OSs. Fully document your
restoration procedures, and periodically retest them, particularly if your
network changes in any important way. Keep backups of your emergency restore
disksyou don't want to be surprised by a bad floppy, which Murphy's Law
guarantees you'd discover at exactly the wrong time.
