Security and Backup
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
Backup strategies
Key Questions: How often should the backups be done? What should be backed up? Where should the backups be stored?
And in terms of planning we need to consider: The value of the data The amount of data stored on the computer Frequency of data changes Type of backup equipment
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
Incremental Backup
Full backup once a week, eg 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
Hardware for backups Small quantities of data:
Removable disks – Removable hard drives or USB Memory sticks
Larger quantities of data: Tape is usual medium; DAT tape drive can store up to 24Gb for about £200 CD-RW/DVD-RW drive using rewritable disks costs around £50.
650Mb CD disks cost about £1 each, DVDs c£2.50.
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.
Grandfather-father-son backups
Update
Transactions for Day 1
Update
Master file (Day 1)
(Grandfather)
Master File (Day 2)
(Father)
Transactions for Day 2
Master File (Day 3)
(Son)
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