Tape Back Up Machine
For companies the
loss of data can be especially serious. Many companies store essential
information such as customer accounts or stock databases on computer.
Loss or corruption of this information could cost a company a lot of money.
If data is very important then appropriate security measures should be
put in place to try and avoid any data loss or corruption. However problems
can still occur:
An employee could accidentally delete a file or a storage device could
fail resulting in data being completely lost.
Data could be changed accidentally. For example an employee may incorrectly
update a set of record in a database. A virus could deliberately change
the contents of a file.
Therefore extra copies of important data should be made on a regular basis.
These copies are known as backups. If the original files become corrupt
then the data can be restored from a backup copy.
USB flash
memory sticks - ideal for quick backups
CD or DVD backup
A Company should have a backup strategy, which
sets out how backups will be made. Often the method used to make backups
will depend upon the type of processing that is being carried out.
Backup Strategies
A backup strategy is a plan that details how backups will be made and
how data will be restored in the event of a system failure.
hard drive backup 
Above are the hard drives available in 2009 - The SATA hard drive which uses revolving disks and the latest Solid State hard drive which has no moving parts this is the latest inovation which is similar to the Flash Memory stick. USB flash memory sticks can also be used for backups, they're quickly incresing in capacity. Sata Hard Drives have capacities measured in Terabytes (1024 gigabytes) and at present work out at the cheapest form storage for large amounts of data.
Many backup programs are available for automatic
backup of your critical data virtually to any type of storage media including
USB flash drives, DVD-RW devices, Tape drives, Hard drives and remote
FTP servers. You can use Backup Software to make a reserve copy of any
valuable data on your system. Special addons are provided to facilitate
the backup of MS Outlook and other messenger files. Restoring is as easy
as clicking a button, but you can also use a number of advanced options.
Backup programs can be also used to synchronize files between two computers
on a network. Backups can be taken of your whole computer -even the operating
system and programs - on the fly. The - on the fly - backup software is
ideal for large concerns that can't afford the computers to be switched
off.
Where should backups be stored ?
There is no point in making a backup copy if the backup may be damaged.
These guidelines should be followed to ensure that backups are stored
safely:
· Store a backup at a site away from the main computer system.In
case of fire etc.
* Protect access to backups
*Keep backups in a warm clean, room so that the will not be damaged.
Normally one selected trained individual should perform backups and keep accurate records of the backups that have been made.
A disaster recovery plan should be in place which describes how the data will be restored.
It's a good idea to make more than one backup
copy. This gives you the extra assurance that if a file is corrupt and
the backup is also corrupt then you have another backup.
Different backup strategies are appropriate for batch, transaction and
real-time systems.
Backups in Batch Processing Systems
In a batch processing system the File Generation or Grandfather-Father-Son
backup method is used. Remember that in a batch processing system all
transactions are entered into a transaction file. This file is then used
to update the current master file to produce a new updated master file.
Backups in Transaction Processing Systems
Backups for a transaction processing system are produced in a different
way to those for a batch processing system. At the end of each time period
a backup copy of the master file is made.
The time period between each backup could be a day or a week. Making
a complete copy of the master file like this is known as file dumping.
The copy of the master file is known as a file dump. Every time an alteration
is made to the master file, since the last backup was made, details of
the alteration are stored in a transaction log file. If the system breaks
down then two things happen :
The most recent file dump of the master file is restored to replace the
corrupt current master file. This contains all of the lost data except
any new transactions made since the backup.
The transaction log file is used to update the restored master file so
that any transactions made since the file dump was produced are restored.
By following this process no data should be lost. If there was no transaction
log file then all of the transactions since the last file dump would be
lost.
Backups in Real-time Processing Systems
The consequences of failure in many real-time systems (e.g. flying a missile/passenger
plane, running a nuclear power station) are immense. There is not a lot
of point in keeping backup copies of data in a real-time system as there
is unlikely to be time to restore backups if anything goes wrong. When
a real-time system is developed the emphasis is placed on ensuring that
the system will not go wrong rather than on designing a backup method
to restore the system if it does go wrong.
Therefore most real-time systems incorporate a lot of spare hardware.
Having much more hardware than you need to do a job means that if some
hardware fails you can carry on doing the job. For example three identical
computers may be used to decide which direction a missile should fly in.
The computers each have a "vote" on which direction the missile
should fly in. Because the computers are identical all three will normally
agree on which direction to take. If one computer goes wrong then the
two working computers will outvote it so the missile will still function
properly despite the failure. If two computers go wrong you are in trouble.
Sometimes backing up data to disk can be useful in real-time systems.
Although this data could not be used to put the system back into its proper
state, it could be used later to analyse why a system failed. The "black
box" that records flight data in an aircraft is an example of this
type of system.