© 2001 by Prentice Hall11-1 Local Area Networks, 3rd Edition David A. Stamper Part 4: Installation and Management Chapter 11 LAN Administration: Backup and Recovery

© 2001 by Prentice Hall 11-2 Chapter Preview Data backup Data recovery Problem detection Problem resolution Diagnostic hardware and software Disaster planning In this chapter you will study:

© 2001 by Prentice Hall 11-3 Data Backup A good LAN-administration policy must provide a method of data recovery to correct data problems. Recovery – If data in a database becomes corrupted or a text file is accidentally deleted, an organization will want to restore the data to a usable state. Restoring from backup is almost always the preferred way to do this. Archiving – Records, or other data, that you no longer regularly need can be archived; that is stored in another location than your hard drive.

© 2001 by Prentice Hall 11-4 Ways in which Data Can Be Corrupted An application program with a logic bug can change data incorrectly. A user can accidentally erase a file.A user can accidentally destroy a file by copying a new file over it. A user can maliciously destroy a file or data in a file. A system failure can leave the database in a state of partial update. A disk failure can destroy data or render it inaccessible. An undetected virus can erase or otherwise destroy data. A bug in system software, such as the database management system, can cause data loss, unreliable results, or data corruption.

© 2001 by Prentice Hall 11-5 Types of Backups Incremental Backup – This type of backup, also called a partial backup, backs up all files that have changed since the preceding backup – With an incremental backup, only files with the archive bit set are backed up. Differential Backup – A differential backup backs all files that have changed since the last full backup. – A differential backup will not reset the archive bit.

© 2001 by Prentice Hall 11-6 Comparison of Incremental and Differential Backups Sunday Monday Tuesday Wednesday Thursday Friday Full backup completed FileA, FileB, FileC FileA, FileD FileE FileA, FielC, FileF FileA FileA, FileB, FileC FileA, FileD FileE FileA, FielC, FileF FileA FileA, FileB, FileC FileA, FileB, FileC, FileD FileA, FileB, FileC, FileD, FileE FileA, FileB, FileC, FileD, FileE, FileF Day Files Updated Incremental Backup Contents Differential Backup Contents

© 2001 by Prentice Hall 11-7 Backup Generations First Generation of Backups Tape 1 Tape 2 Tape 3 Tape 4 First Generation of Backups Tape 2 Tape 3 Tape 4 Tape 1 Grandfather Father Son Unused Grandfather Father Son Next to Be Used

© 2001 by Prentice Hall 11-8 A Sample Backup Retention Policy Back up all files changed since the backup of the preceding day. Make two copies; store one copy off-site. Back up all files. Make two copies; store one copy off-site. Back up all files as of midnight, December 31. Back up all files as of midnight at the end of the fiscal year. Make two copies; store one copy off-site. Backup Policy Daily Weekly End of year Retention Policy Retain weekly backups and daily backups for 1 month. Retain the first backup of each month for 1 year. Retain the end-of-year backups for 5 years.

© 2001 by Prentice Hall 11-9 Backup Frequency Static data should be backed up at least twice, and the two versions should be stored in separate locations. Dynamic files must be backed up more often. Some installations do daily backups; others find that a weekly backup is adequate. Failure rates and timeliness of recovery are factors to consider as well. If failure rates and the need to immediately return to operational status are high, then backups should be more frequent than if failure is uncommon and timeliness is not a major factor.

© 2001 by Prentice Hall How and When to Make Backups Because most of today’s LAN backup utilities do not provide data integrity protection for on-line backups, it is usually best to create the backups when data is not being modified. In many situations, the LAN is not used at all over night. Unattended backups are possible through the backup software itself or through separate software utilities. If a company’s software does not provide unattended backup, the LAN administrator may still be able to start the backup remotely.

© 2001 by Prentice Hall Data Inconstancy During File Backup Time Record A-$1,000 Record A-$500 Record X-$1,500 Record X-$2,000 Record X-$1,500 File 1File 2 Backup Starts Record A-$1,000 File 1 Backup Completes Transaction Starts Transaction Ends File 2 Backup Begins Record X-$2,000 Record A-$500Record X-$2,000 Backup is inconsistent, Record A show a balance of $1,000 and Record X shows a balance of $2,000

© 2001 by Prentice Hall Use of a Before Image in a Transaction Time $1,000$500 File 1File 2 Before Images 1. Capture before image of record being changed. Begin Transaction 2. Deduct $300 from record and write new balance. File 1 $1,000 $ Capture before image of record being changed. File 2 $500 $ Add $300 to balance of record in File 2. End Transaction If for some reason the transaction cannot be completed, the before images are used to back up database changes that have been made and thus restore the integrity of the database.

© 2001 by Prentice Hall Database After Images Time $1,000$500 File 1File 2 After Images 1. Capture after image of record being changed. Begin Transaction 2. Deduct $300 from record and write new balance. File 1 $ Capture after image of record being changed. File 2 $ Add $300 to balance of record in File 2. End Transaction If a failure occurs that destroys data in File 1 and/or File 2, the current state of the database can be reconstructed through backup tapes and the after images of completed transactions. The backup is first restored, and then the after images are written in chronological order to bring the database forward to a current, consistent state. Transfer $300 from File 1 to File 2.

© 2001 by Prentice Hall Synchronization of Backups and the After-Image Audit Trail Time After-Image Audit Trail Record 1 File 3 Record 20 File 2 Record 2003 File1 Record 992 File 1. Backup begins. Current after-image audit trial is closed. Backup Tape Backup Tape Backup completes. Record 123 File 4 Record 1209 File 1 Record File 1 Record File 3. After-Image Audit Trail New after-image audit trail started. The new after-image audit trail is synchronized with the backup just completed

© 2001 by Prentice Hall Recovery Steps Identify and correct the source of the problem. Back up the data that has been corrupted. Restore the most recent, valid backup version of the lost data. Bring the data forward I time until it is both consistent and current. Run diagnostic tests to ensure that the recovery has indeed corrected the problem and that the data is consistent. Document the problem experience, corrective actions, and problems encountered during recovery. Create and implement procedures to prevent similar future occurrences.

© 2001 by Prentice Hall Disaster Planning A disaster plan addresses situations that disable major portions of the system. Disaster planning covers situations arising from fires, earthquakes, floods, and intentional acts of system destruction. A key aspect of a disaster plan is off-site data storage and hardware replacement. After planning for software and data recovery, the LAN administrator should also have plans for rebuilding the system. This may include items such as sources of compatible hardware, identification of hardware at other corporate locations that might be borrowed for emergency use, identification of alternative locations for temporarily or permanently installing the new system, and identification of companies specializing in all aspects of LAN hardware, software, cabling, installation, and data recovery.

© 2001 by Prentice Hall Items Included in Disaster Plan Amount of insurance coverage for software, hardware, and cabling Insurance carrier Steps required to begin replacing/repairing insured components Location of off-site storage of software Currency of off-site software backups Device used to create off-site storage Sources of replacement software Companies specializing in recovering data from damaged media (backup tapes and disk drives) Location of off-site storage of data Currency of off-site data backups Device used to create off-site data storage Methods to bring off-site data forward to a current status Companies specializing in recovering data from damaged media (backup tapes and disk drives) Insurance Software Data

© 2001 by Prentice Hall Items Included in Disaster Plan (cont.) Workstation configurations Server configurations LAN topology/wiring diagrams Sources of replacement hardware Sources for repairing broken hardware Location of spare hardware Alternative locations for establishing a new network environment Minimum requirements for establishing a new network environment Names of companies specializing in data recovery, setting up a new network, data entry, cabling repair, and so on Hardware Environment Outside Help