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)