Backup and Restore

Backup  Databases live in a fragile environment  Machines can fail  Disks can fail  Programs can fail

Backup  Backup creates an image of the database  This image can be on: –Disk –Tape –CD/R –Other writeable media

What the Backup Does  Remember that the database is made up of 1 or more files that are made up of 8K pages  Backup reads these 8K pages and writes them where specified  Backup works only at the 8K page level. It knows nothing about rows and columns

Types of Backup  Full Backup  Differential Backup  Transaction Log Backup  File and Filegroup Backup

Full Backup  Backs up all pages in a database  Normally a transaction log backup would also be done  Restore would require full backup and trans log backup

Differential Backup  Backs up only pages that have been changed since the last backup  The page header has a flag indicating that the page is ‘dirty’  Normally a transaction log backup would be taken  Restore would require last full backup, all differential backups and trans log backup

Transaction Log Backup  Makes a copy of the the transaction log  Does not copy any database pages  Is needed when the transaction log becomes full

File Backups  File backups are similar to database backup except they operate at the file level rather than the database level  Can be full or differential  Because they operate at the file level, several can run concurrently, speeding up backup time

Dump Device  Also called Backup Device  Before a backup can be run a dump device must be defined  This is the location or device where the backup file will be written  Is not required with v& and SQL Srvr 2K, but works

Create Dump Device sp_addumpdevice = ] 'device_type', = ] 'logical_name', = ] 'physical_name' [, { = ] controller_type | = ] 'device_status' } ]

Examples EXEC sp_addumpdevice 'disk', 'mydiskdump', 'c:\dump\dump1.bak' EXEC sp_addumpdevice 'disk', 'networkdevice', '\\servername\sharename\path\filename.ext' EXEC sp_addumpdevice 'tape', 'tapedump1', '\\.\tape0'

Backup Command  BACKUP DATABASE { database_name } TO [,...n ]  BACKUP DATABASE { database_name } [,...n ] TO [,...n ]  BACKUP LOG { database_name } {TO [,...n ] }

Restore  Restore takes the contents of a full backup and optionally differential backups and log backups and rebuilds the database  Restore writes 8K pages with no knowledge of rows or columns

Restore Command  RESTORE DATABASE { database_name } [ FROM [,...n ] ]

Backup Considerations  The backup is the final lifeline for a database  A database should be backed up on a regular basis  Each application may have a different meaning for regular  Once per day, per week, or per month are not unusual periods

Backup Considerations  Given the option you should not backup to the same physical disk that the database exists on (what happens if the disk goes out)  You should have a backup separate from the server (tape?, networked drive?)  You should have a backup that is off-site (professional offsite, your closet at home)

Backup Consideration  Fight to make stand alone backups  Don’t allow backups to be skipped  Keep several backups  A pattern of full backup and differential backups can be a successful strategy  If using tape, get quality tapes and don’t overuse them (how much is the data worth?)