Chapter 11 Backups

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Chapter 11Backups

• Unix System Administration

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Backup. Why? Because We Like You.

• Why backup at all?
• Restore from data loss
• Disaster recovery
• Archival of old data - possibly for legal reasons

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In the Media...

• Backup devices/media
• Tape
• Optical (MO)
• CDROM (CD-R, CD-RW)
• DVD-R, DVD-RW, DVD-RAM
• Removable Disk (Zip, Jaz, floppy?)
• Paper?

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Mr. Nixons Preferred Media

• There are a variety of tape formats to choose
  from
• QIC Cartridge 60MB per tape
• 8mm - 2 to 20GB per tape (native)
• 4mm - 1.3 to 24GB per tape (native)
• DLT - Digital Linear Tape - 20 to 35GB per tape
  (native)

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8mm - Coming to Video Soon

• Cartridge-based tape derived from the Sony
  Handycam type video tape
• Handycam tapes will work, but data 8mm tapes are
  of higher quality

Drive Model Tape Length Capacity 8200
112 2.3Gb 8500 112 5 8505 112 5 8505XL 160
7 8900 (Mammoth) 170 20
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Sometimes Smaller Is Better

• 4mm
• Based on DAT (Digital Audio Tape) format

Tape Format Tape Length Capacity DDS-1 60 1.3GB
DDS-DC 90 2 DDS-2 120 4 DDS-3 125 12
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Ill Have a DLT on Toast

• DLT - Digital Linear Tape
• Tape to reel format, that is, the tape is spool
  to another reel in the drive. It is not
  cartridge format.
• 100 duty cycle

Tape Format Capacity DLT 4000 20GB DLT
7000 35GB DLT 8000 40GB
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Give Your Data a Big Hug

• Compression
• 8mm, 4mm and DLT drive perform hardware
  compression
• Marketing usually uses 21 ratio
• Actual is usually 1.81
• Compression is based on the type of data you are
  backing up. Text most compressible and
  pre-compressed data least compressible

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Do and Dohs

• Do
• Test your backup periodically
• Store copies of data offsite
• Label your backups so you know whats on them
• Dohs
• Store your tapes near magnetic or electromagnetic
  sources
• The Earths background radiation can eventually
  erase magnetic tapes

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Cage Match Stackers Vs. Autoloaders Vs. Jukeboxes

• Stacker autoloader
• Sequential tape access
• Feeds next tape into drive when on is ejected
• Jukebox
• Random access to tapes in library

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Backup oftware

• Commercial
• Veritas Netbackup
• Legato Networker
• IBM ADSM
• Free or OS Provided
• tar
• cpio
• dd
• dump/restore

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OS Backup Tools

• tar - Tape Archiver
• tar cf /dev/rmt/0 filea fileb filec
• tar xf /dev/rmt/0
• tar tf /dev/rmt/0
• cpio - copy in/out
• similar to tar, ATT specific
• dd - disk duplicate
• dd if/dev/rmt/0 of/dev/rmt/1
• dd ifboot.img of/dev/rdiskette

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Whod Want To Restore a Dump?

• Dump and Restore
• ufsdump and ufsrestore in Solaris
• Primarily Used to backup partitions/slices
• Maintains levels of backups for doing
  incremental dumps
• Restore program has option for interactive shell
  like file browsing
• Dump/Restore can be used to backup a
  partition/slice to another partition/slice

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Dump Examples
ufsdump 0ubf 126 /dev/rmt/0n /dev/rdsk/c0t0d0s0 uf
sdump 5ubf 126 /dev/rmt/0n /dev/rdsk/c0t1d0s7 ufsr
estore ifs /dev/rmt/0 2 Slice-to-Slice
Dump newfs -v /dev/rdsk/c0t1d0s6 mount
/dev/dsk/c0t1d0s6 /mnt ufsdump 0f -
/dev/rdsk/c0t1d0s7 (cd /mnt ufsdump 0f -)
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Managing Your Tape Worm

• mt - Magnetic Tape
• mt -f /dev/rmt/0 rewind
• mt -f /dev/rmt/0 erase
• mt -f /dev/rmt/0 offline
• mt -f /dev/rmt/0 status
• mt -f /dev/rmt/0 fsf

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Good Ol ATT Vs. BSD Again

• /dev/rmt/0 - ATT device name
• Tape head is left positioned BEFORE filemark
• You must explicitly move it past the filemark or
  subsequent reads will return 0, -1 or EOF
• /dev/rmt/0b - BSD device name
• Tape head left positioned AFTER filemark
• Data is read/written from that point

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Q Du Jour

• What could happen if you mix ATT and BSD tape
  device names when putting multiple backups on a
  tape?
• Whats a holey file?

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Holey Files Batman!

• When a file says it is using more disk space than
  it actually is.
• Output of du doesnt equal what ls -l says.
• Seeking way past the eof and writing data no
  data exists between the old eof the new data.
• Tar and cpio can be fooled into backup this empty
  space, dump/ufsdump can handle this oddity.