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Backup & Restore

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  1. Backup & Restore • Objectives • to understand Unix backup strategies • Contents • why have backups • backup terminology • backup media • backup utilities • issues about backup security • Practical • to perform backups • Summary

  2. Why Backup? • Backups help recover data in the event of system failure • Allow users to recover accidentally (or deliberately) corrupt or deleted files • Used to retain data while systems are upgraded • Backups are also be used for transferring data between non-networked machines BACKUPS ARE USELESS IF THEY CANNOT BE RESTORED

  3. When to Backup • Use cron to schedule backup scripts to run overnight • Backup changing data every day • possibly use a full backup on one day • and incremental backups on the rest • make sure you change tapes every day • don't backup to the same tape all the time # more backup.full DAY=`date +%a` cd / touch /var/adm/backup.full find etc home var -print | \ cpio -ocvBO /dev/st0 2>/var/adm/log.$DAY # more DAY=`date +%a` cd / find etc home var -newer /var/adm/backup.full -print | \ cpio -ocvBO /dev/nst0 2> /var/adm/log.$DAY

  4. Where to Store Backups • Store backups in a lockable fireproof safe • if you don't have one buy one, they're not expensive • Unix backups are insecure • there are no access controls • anyone with physical access to the media can restore the data • Take backups and archives off-site • backups are no good if they are burnt/flooded with the computer systems • however, remember that data is confidential • Don't keep backups immediately next to the machine • at the very least put the backups in a different building or room

  5. What to Backup? • Backup those files which change on a daily basis: /etc Unix configuration file /var Unix files which vary on a day to day basis /home user files • only backup the entire system when needed • Backup the entire system on a regular basis • especially before updating the system • before preventative maintenance or moving the hardware • Be careful with database systems • databases usually involve several files which must be consistent • stop database systems before backing up their files • some databases have a backup mode used when the system cannot be taken down for backups • databases using raw disks for storage will provide their own backup

  6. Backup Media • Traditional backup media is magnetic tape • reel-to-reel (½" or 9-track) • cartridge tape (¼" or SCSI tape) • video-8 (Exabyte) • DAT (Digital Audio Tape) • DLT (Digital Linear Tape) • Other media include • removable disk packs (Bernoulli) • WORM disk (Write Once Read Many optical disks) • recordable CD (CD-R/DVD) • rewriteable optical disk (MO, phase change)

  7. Magnetic Tape • Magnetic tapes susceptible to magnetic fields • power cables, motors, magnets, etc. • Cartridge media degrades with time and use • 2 year life span and should be read every 6-12 months • replace tapes after 10 writes (20 at most!) • DAT, DLT and Exabyte will last longer • but still have a limited life • Needs careful storage • temperate and humidity controlled • sunlight (don't leave on a windowsill) Don't compromise your backups by using cheap or worn media

  8. Optical Disks • Optical disks have advantages over magnetic tapes • digital recording • reliable & robust media • compact media • can be treated as disks (no need to use backup utilities) • Also have disadvantages • smaller capacity • more expensive media/drives (less true as technology advances) • WORM or CD-R is the only choice for long term archives • data that must be kept for more than one year

  9. Unix Backup Terminology • Archive • full backup taken off-line (deleted from the system) • Image backup • complete copy of a disk or partition • Full backup • complete directory backup by files • Incremental backup • files changed since last full or incremental backup • Dump levels (0-9) • files changed since last backup at same or lower dump level • level 0 dump is a full backup

  10. Backup Utilities • File oriented utilities cpio - copy to I/O tar - tape archive and restore • Filesystem utilities dump - backup linux filesystems WARNING! OBSOLETE! restore - restore linux dump WARNING! OBSOLETE! dumprx - dump Veritas filesystems restorerx - restore Veritas dump • Device level dd - direct device access(image backups) • Proprietary utilities • yast backup, SuSE backup • some manufacturers provide their own utilities (AIX: backup & restore) • if you use these you are tied to that manufacturer • Third party Applications

  11. Tape Archive and Restore • Use tar for quick and simple backups • not flexible enough for sophisticated backup strategies • Files are written to the archive in tar format • directory pathname and inode information • user, group and permission information • creation and modification times SCSI Tape device in Linux are usally called: /dev/nst[0-31] rewind /dev/st[0-31] no rewind Dencity modes: -, a, l, m # cd /home/radar # tar cvf /dev/st0 . # tar tvf /dev/st0 # cd /tmp # tar xvf /dev/st0

  12. list of files from stdin writes archive to stdout cpio -o archive read from stdin table of contents to stdout cpio -it archive read from stdin files restored according to archived pathname cpio -i Copy to I/O • Use cpio for system backups • supports flexible and sophisticated backup strategies • Files are written to the archive in cpio format • directory pathname and inode information • user, group and permission information, creation and modification times

  13. Options to cpio • General options -v verbose mode -B use large blocks -Cn use blocks of n bytes -c use ASCII headers (always use this option) • Specify I/O devices with -Ofile for better handling of multi-volume media when archiving -Ifile for better handling of multi-volume media when restoring • Input (restore) options -t list table of contents rather than restore files -d create directories if needed -u unconditionally restore files -m retain file modification times

  14. Exercise - Using cpio • Explain the purpose of the following commands? # find . -print | cpio -ovcB >/dev/rmt/0m # cpio -itvcB </dev/rmt/0m # cd /tmp # cpio -ivcdumB </dev/rmt/0m # cd / # find etc home var -print | cpio -ovcB -O /dev/rmt/0m # cd /tmp # cpio -ivcdmB -I /dev/rmt/0m 'etc/init.d etc/rc*.d'

  15. Summary • Unix provides basic utilities for performing backups tar, cpio yast backup dump & restore dumprx & restorerx dd • Unix backups are written to the media with their file attributes and pathnames • Unix backups are insecure, there are no access control restrictions Keep all backups in a locked temperature and humidity controlled environment • Backups are vital to system integrity - keep offsite backups if possible