1. Security and Backup

2. 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

3. 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

4. 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

5. 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

6. 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.

7. 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.

8. 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)