Chapter 11

LAN Administration: Backup and Recovery

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Data Backup

The data you have on your network is valuable and it would be costly if destroyed.  In this chapter we look at different ways to backup your data.  Before we look at these methods lets talk about why we would need to do backups.  We learned in chapter 7 that we can make our data redundant by using RAID or duplexed servers.  This is great if we have a hardware failure, but what happens if a user accidentally deletes a file they are working on.  That deletion would appear on all RAID drives and duplexed servers.  In this case the user will need to manually recreate the file.  Below is a list of situations which might occur that could cause data lose:

  • User unknowingly deleting files/folders

  • Malicious users deleting files/folders

  • Virus deleting files/folders

  • A software bug causing corrupt files/folders

  • A system crash causing corrupt files/folders

  • A hacker attacking the system deleting files/folders

  • Hardware crash

  • Natural Disasters

In each of these situations if a backup is done you can recover the data.  A backup is a snapshot of data at a specific time stored on removable media.  The removable media should be stored at an offsite location.  The key to the backup process is the Archive Bit.  This archive bit lets the backup software know the status of the files/folders it is trying to

Archive Bit in Windows 2000

backup.  If it is turned on it needs to be backed up, If it is off it has not changed since the last full backup.  The OS will change the archive bit from Off to On when files or folders are changed.

When backing up your data there are different types of backups you can do. 

  • Full Backup: Backs up all files on a server.  When it does this it will turn off the archive bit on all files.

  • Incremental Backup: Only backs up files which have the archive bit turned on.  Once it backs up a file it will reset the archive bit to off.

  • Differential Backup Only backs up files which have the archive bit turned on.  This Will Not change the archive bit.

  • Copy: Backs up all files on a server.  This Will Not change the archive bit.

  • Daily: Backs up only files that changed that day.  This Will Not change the archive bit.

  • Working Set: Backs up only files last accessed in (x) days.  This Will Not change the archive bit.

  • Archive: Copies selected files then deletes the originals. 

Backup Type What Files does it backup? Archive Bit Status After Backup
Full Backup All Files and Folders Off
Incremental Backup Files and Folders with Archive Bit On Off
Differential Backup Files and Folders with Archive Bit On On
Copy All Files and Folders Unchanged
Daily Files and Folders modified that day Unchanged
Working Set Files and Folders last accessed in (x) days Unchanged
Archive All Files and Folders N/A - Original Files Deleted


Restoring data can happen in a few different ways.  If the data that needs to be restored is user data it can either be restored from tape or manually recreated.  If an application need to be restored you can reinstall the software from the original media.  Sometime it is faster to reinstall software then it is to try and restore from tape.  Because of this on some servers you may want to only backup user data and not the OS itself.

Some other uses of backups might be low-cost bulk storage or data interchange. 

Backup Hardware, Software, and Procedures

The most popular backup media is a tape.  These tapes usually go in to  a drive that has a SCSI interface. 

To the left we see DAT tapes and to the right we see DLT tapes.  These two types of tapes or not compatible with each other. 

When backing up to tape you'll want to have multiple tapes in a backup rotation.  This allows you to restore data that may have been deleted or damaged awhile ago.  Sometimes a file won't appear to be corrupt until weeks after it was damaged.  If you only had one tape and you overwrote it each week when you did a backup you wouldn't be able to get to the needed data

For example you may have six sets of five tapes.  One set would contain 5 tapes for each day of the week.  This would allow for six weeks worth of backups.  This proves to be useful as many times it might take someone a while to find out a file is missing or corrupt. 


The type of data you have also helps to determine your backup schedule.  If you have a lot of static data you may not need to backup on a daily basis.  But if your data is dynamic (changing all the time) then you are going to want to backup as often as you can.  Another thing you will need to consider is what time are you going to perform a backup.  You will want to do it when there is very little or nothing being used on the network.  For most organizations night would be the time to perform a backup.

Backup software will allow you to create a backup schedule so all you have to do is change the tape.  It will also keep a log to show you if there were errors, and it will allow you manage media to track when it should be replaced.  Some times there will have the capability to backup files that are in use or maybe even do a virus scan of files as well.  Veritas makes a program called Backup Exec which come in many different versions for different network operating systems. 

DBMS Recovery

A database is a little different when it comes to backup and recovery.  After you do a backup of a database logs are created that record all transactions.  If the database is damaged you can restore the database then process the logs to bring it back to the latest status.  Once you do a backup the logs will be flushed and new ones are started.

Disaster Planning

In the event of a major disaster on site you will want to have a plan in place to quickly bring the network to operational status.  Here is a list of things you will want to include in your disaster plan.

  • Insurance:

    • Amount of insurance coverage for software, hardware, and cabling.

    • Insurance Carrier.

    • Steps required to begin replacing/repairing insured components.

  • Software:

    • Location of off-site storage of software

    • Currency of off-site software backups

    • Device used to create off-site storage

    • Sources or replacement software

    • Companies specializing in recovering data from damaged media (backup tapes and disk drives)

  • Data:

    • Location of off-site storage of data

    • Currency of offsite data backups

    • Device used to create off-site data storage

    • Methods to bring off-site forward to current status

    • Companies specializing in recovering data from damaged media (backup tapes and disk drives)

  • Hardware:

    • Workstation configurations

    • Server configurations

    • LAN topology/wiring diagrams

    • Sources of replacement hardware

    • Sources for spare hardware

    • Location of spare hardware

  • Environment:

    • Alternative locations for establishing a new network environment

    • Minimum requirements for estaor blishing a new network environment

  • Outside Help:

    • Names of companies specializing in data recovery, setting up a new network, data entry, cabling, repair, and so on

More Information


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