The aim of producing a backup strategy is to make sure that a computer system can be returned to its original state if data has been lost or corrupted. - PowerPoint PPT Presentation

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The aim of producing a backup strategy is to make sure that a computer system can be returned to its original state if data has been lost or corrupted.

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Title: The aim of producing a backup strategy is to make sure that a computer system can be returned to its original state if data has been lost or corrupted.


1
Ch 15 A2 BACKUP STRATEGIES
  • The aim of producing a backup strategy is to make
    sure that a computer system can be returned to
    its original state if data has been lost or
    corrupted.

2
Backup Strategy Recap ICT2 Ch19
A backup strategy is put in place to avoid
permanent data loss and to ensure the integrity
of stored data ie can get back to a previous
version and build up the data correctly if
current data found to be in error.
  • Factors that should be considered in a backup
    strategy
  • Selection of storage medium depends on volume of
    data
  • Frequency of backup depends on how often the data
    is updated
  • No. of backup copies kept depends how often data
    is updated
  • What will be copied full (all data) or
    differential (just changes)
  • Recovery procedures how quickly correct data is
    needed
  • Location of backup how secure is this data?

3
Recovery Procedures ICT2 Recap Ch19
A backup strategy needs a well documented and
tested recovery procedure to ensure backup data
is restored properly
  • Factors that should be considered in a recovery
    procedure
  • A well documented procedure that allocates roles
    and responsibilities to staff.
  • Availability of alternative hardware and
    accommodation if the originals have been
    destroyed.
  • Availability of original software such as the
    customised operating system and application
    programs!
  • That up-to-date backup data is readily available

4
Different types of system require different
strategies
Batch processing systems Defn A large number of
similar paper documents are typed up onto a
transaction tape. The transaction tape updates
the master file at a regular set time. Eg
Payroll timesheets are typed into a transaction
file and update the employee master file each
Friday night and produce wage cheques and
payslips.
How would the Son file be regenerated?
5
Different types of system require different
strategies
Online backup of small/medium interactive
transaction systems Transactions are typed in
and processed immediately before the next
transaction is entered. Eg Paying a gas bill a
business cant afford to lose even a small amount
of data but can lose some operational time while
data is restored from backup. There is no
prepared transaction tape so the system creates a
record on an online transaction log as each
transaction is typed in. The master file is
backed up every night.
If the system crashes the son master file is
restored from last nights father backup after
adding the days transaction log to it.
6
Different types of system require different
strategies
Online backup of large important interactive
systems Some large volume data systems are
critical to the operation of a business eg A bank
customer accounts file. The bank cant afford to
lose even a small amount of data or lose
operational time while data is restored from
backup. So the backup must be taken after each
online transaction and written to easily accessed
backing storage ? disk. This is called Disk
Mirroring and is a type of RAID.
Disk mirroring storing identical data on 2
different disks at virtually the same time
(RAID). Disks are in different locations.
7
Selection of appropriate backup medium
Its not just size that matters but the way
backing store is used too!
Digital Audio Tape (DAT)
Selection depends on The capacity (amount of
data stored on the tape/disc) the speed of
transfer and the cost of the medium should be
considered.
Disk mirroring (RAID)
  • Type of medium
  • Floppy discs not appropriate for most companies
    as only holds 1.44Mb of data (approx 144,000
    characters of data)
  • DAT is magnetic tape and holds 12-20GB with
    transfer speeds up to 150Mb per minute. OK for
    small companies who may not mind being without
    data for up to a day while the data is restored.
  • Disk mirroring is fast and backup always
    up-to-date, but expensive

8
Selection of appropriate backup drive
If tapes are used to back up data then they
usually have to be manually loaded into the tape
drive before backup can take place. This is OK if
just using one backup tape as it can be preloaded
and the backup program automatically runs
overnight without anyone needing to be there.
However if there is a lot of data to back up then
two or more tapes will be needed. This requires
someone to unload and load them as the backup
program runs sleepless nights for someone!
A tape library is a device that makes unattended
large scale backups possible. It consists of a
tape drive and a robotic device that can move
tapes in and out of the drive.
9
Selection of Backup Location
Backup files must be kept in a separate location
to the original file in case of fire or theft.
However if they are kept a long distance away
the time needed to get the backups increases the
time taken to restore files after a disaster.
  • Sometimes a fireproof safe is used to store
    backups in the same building
  • Sometimes they are kept at another building owned
    by the company
  • In large cities firms exist that provide a backup
    service. They come and collect the backups daily
    and store at their own premises. They also
    provide correctly labelled tapes. If disaster
    strikes they will return the backups immediately.
  • Remote backup similar to no3 but backup is
    transmitted over a WAN to the firm. Data can be
    vulnerable and needs to be compressed and
    encrypted.

10
Scheduling Types of Backup
Full Backup A full copy of the system is copied
to tape each night. A different tape is used each
day. Restoration is easy as the system can be
restored from just one tape. However if the
volume of data is large then the backup may take
many hours and might not be complete before the
next days business begins. Differential Backup
One full copy of the system is copied to tape
over the weekend. Only changes to the data are
copied to tape during the week. This allows the
data to be restored with a maximum of just 2
tapes. It takes longer to restore the original
data as the changes must be applied to the full
weekend backup. Incremental Backup - One full
copy of the system is copied to tape over the
weekend. Only changes to that days data are
copied to tape during the week. This allows the
data to be restored with a maximum of 6 tapes. It
takes much longer to restore the original data as
each daily tape must be applied in order to the
full weekend backup. (However the actual backup
is faster as changes only copied once.)
11
Tape rotation methods
It is bad practice to only use one backup tape
if this breaks?!. A number of generations of
backup will require careful labelling and a tape
rotation system is used to ensure that correct
versions are kept. (Legal obligations can dictate
how long data is kept) The Grandfather, Father,
Son Method If data is updated on a daily basis
then Tapes are labelled by the day of the week
with a different tape for each Friday in the
month and a different tape for each month of the
year. (Assuming no data changes on Sat or Sun) So
Mon, Tue, Wed Thur tapes are overwritten weekly
and Fri tapes are overwritten monthly. This still
means there are over 20 generations of current
backup tape for this system A written backup log
should be kept of backups taken with date, time,
name of labelled tape, name of person who did
backup.
12
Questions how well have you listened!!
  • What is the main method of tape rotation?
  • What are the 3 types of scheduling backing up
    data?
  • What is a tape library?
  • How would you back up data from a batch process?
  • How would you back up data from a critical
    interactive transaction process?
  • How would you back up data from a non-critical
    interactive transaction process?
  • What are the advantages and disadvantages of
    backing up data remotely via a WAN?
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