Security and Backup

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Security and Backup
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Introduction

• A back-up strategy must cover all eventualities
• Accidental damage
• Equipment failure
• Deliberate damage
• It must consider
• Security measures
• Personnel policy to cover data security and
  employee codes of conduct
• Directors are responsible for security of all
  company assets

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Backup strategies

• Key Questions
• How often should the backups be done?
• What should be backed up?
• How much data is there?
• What storage medium should be used?
• Where should the backups be stored?
• Who will be responsible?
• Organise
• Keep backup log
• Test backup recovery

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Full Backup

• A copy of all the files on the fixed disks
• Very safe, and simple to restore
• But, time-consuming and computer facilities will
  be off-line while this is happening.
• Example of large-company strategy
• Service agreement to have engineers available
  within specified time
• mirrored disks on file server simultaneous
  update to both disks
• Four tapes for Monday to Thursday stored in
  fireproof safe in office
• Process starts at same time every night
• Backup log checked every morning
• 3 Friday tapes - Friday tape taken off-site,
  next Friday the oldest Friday tape is used
• Hardware maintenance performed by Service Agency
• Occasional tape-restore test

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Incremental Backup

• Full backup once a week, e.g. Monday
• On other days, only those files that have been
  changed during the day are backed up
• Must be labelled carefully
• Less time-consuming, but
• More complex to restore as all backups have to be
  restored in the correct sequence

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Hardware for backups

• Small quantities of data
• Removable disks e.g. Iomega Zip drives 100
  and 250Mb diskettes
• Larger quantities of data
• Tape is usual medium
• DAT tape drive can store up to 24Gb for about
  600
• CD-RW drive using rewritable disks costs around
  200. 650Mb disks cost about 2 each.

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On-line back-up (RAID)

• RAID (Redundant Array of Inexpensive Disks). This
  technology enables data to be written
  simultaneously to several disks.
• Three copies of a database may be held two
  locally and one on a remote system.
• If one system fails then data can still be used
  on either of the other two.

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Grandfather-father-son backups
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Questions

• Try, as a group, the questions 1 and 2 in
  Heathcote Pg 295
• I will give you the answers in a moment