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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. Why Backup?. Backups help recover data in the event of system failure

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backup restore
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
why backup
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

when to backup
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 backup.inc

DAY=`date +%a`

cd /

find etc home var -newer /var/adm/backup.full -print | \

cpio -ocvBO /dev/nst0 2> /var/adm/log.$DAY

where to store backups
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
what to backup
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
backup media
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)
magnetic tape
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

optical disks
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
unix backup terminology
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
backup utilities
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
tape archive and restore
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

copy to i o

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
options to cpio
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

exercise using cpio
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\'

summary
Summary
  • Unix provides basic utilities for performing backups

tar, cpio

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
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