| Good backups are critical to the health
of a network. The value of a good backup system is most appreciated
when it is needed in an emergency. When a system is down and data
becomes unavailable, people are unable to get their work done and
companies are unable to do business.
A well-managed network includes regular
backups performed by a system administrator. Network administrators
who do not have good backups or are unable to restore data quickly may
lose their jobs because of it. Having a good backup system and a
tested restoration process can save an organization millions of
dollars and thousand of hours in lost productivity. Data can be lost
or corrupted due to many things, including:
Hard Disk Failure - Disk drives
(floppy, Hard disks and CDs) are the most likely components in a
computer to fail since they are electromechanical devices with moving
parts that wear. Most other components in a computer, such as the
CPU and RAM, are electronic with no moving parts. When a hard drive
fails, some or all of the data on the drive can be damaged or become
inaccessible. This is why fault tolerant disk systems such as RAID 5
(Redundant Array of Independent Disks - Level 5) were developed for
network servers. RAID 5 combines three or more drives as a group so
that if one fails, the others take over. The bad drive can be replaced
with no loss of service to the users. Another fault tolerant technique
is mirroring, which uses two drives with the second drive storing the
same data as the first. One of the drives can fail and the other will
take over. Fault tolerant disk systems are the first line of defense
in a solid backup strategy.
File Corruption - File corruption can occur due to many things
including improper system shutdown, magnetic fields near the data or
when an area of the disk goes bad. In any case, the data becomes
inaccessible. A good backup system will allow the administrator to
find and recover a specific file.
Malicious Destruction - Files can also be lost due to
intentional destruction of data. File deletion can result from
disgruntled employees, virus attacks, or hackers who can remotely
access a system. Damage can vary from deletion of one or two files to
the loss of all data on a hard drive. Most virus attacks come from the
Internet and firewalls can help in some cases. Fortunately, UNIX is
relatively immune to virus attacks, but most other network operating
systems and desktop operating systems are not. For non-UNIX operating
systems, virus protection software can be installed to help detect and
eradicate viruses before they do damage. Firewalls can also help in
the case of hackers by detecting and blocking the attacks. In the case
of a disgruntled employee deleting data, the best defense is having a
good backup.
Disasters - Disasters such as
fires and floods can destroy computers, data centers, and entire
buildings. In the previous chapter on security, we discussed the
importance of a disaster recovery plan. If a fire were to destroy a
place of business, how would they recover? How much would it cost them
per day or per hour to not be able to do business? Backups are a big
part of a disaster recovery plan. To get systems back up and running
quickly, it is important to have good quality current backups of
critical data. The backups should also contain copies of operating
system and applications software and should be stored offsite at a
nearby location.
Accidental Deletion / Overwrite
- It is not uncommon for a user to accidentally delete a file. Files
deleted from the command line cannot be recovered except from a
backup. If the file cannot be recovered from a backup, it may need to
be recreated causing lost productivity. Files deleted using CDE File
Manager can be recovered from the Trash Can. Work can also be lost due
to accidental overwrites. This occurs when a user makes a copy of a
file and then makes substantial changes to it. They then open the
original file and save it over the one with changes. It is also
possible to overwrite files when copying them from one location to
another where the file already exists. When this occurs the only way
to recover the original file is from data backups.
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