Chapter 11Backups

Unix System Administration

Backup. Why? Because We Like You. Why backup at all?

• Restore from data loss• Disaster recovery• Archival of old data - possibly for legal reasons

In the Media...

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

Mr. Nixon’s Preferred Media

There are a variety of tape formats to choose from…• QIC Cartridge 60+MB 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)

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 qualityDrive Model Tape Length Capacity

8200 112 2.3Gb

8500 112 5

8505 112 5

8505XL 160 7

8900 (Mammoth) 170 20

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

I’ll 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

Give Your Data a Big Hug

Compression• 8mm, 4mm and DLT drive perform hardware

compression• Marketing usually uses 2:1 ratio• Actual is usually 1.8:1• Compression is based on the type of data you

are backing up. Text = most compressible and pre-compressed data = least compressible

Do and Doh’s Do

• Test your backup periodically• Store copies of data offsite• Label your backups so you know what’s on them

Doh’s• Store your tapes near magnetic or electromagnetic

sources• The Earth’s background radiation can eventually

erase magnetic tapes

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

Backup $oftware Commercial

• Veritas Netbackup• Legato Networker• IBM ADSM

Free or OS Provided• tar• cpio• dd• dump/restore

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, AT&T specific

dd - disk duplicate• dd if=/dev/rmt/0 of=/dev/rmt/1• dd if=boot.img of=/dev/rdiskette

Who’d 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

Dump Examples

ufsdump 0ubf 126 /dev/rmt/0n /dev/rdsk/c0t0d0s0

ufsdump 5ubf 126 /dev/rmt/0n /dev/rdsk/c0t1d0s7

ufsrestore 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 -)

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

Good Ol’ AT&T Vs. BSD Again

/dev/rmt/0 - AT&T 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

Q Du Jour

What could happen if you mix AT&T and BSD tape device names when putting multiple backups on a tape?

What’s a “holey” file?

Holey Files Batman! When a file says it is using more disk space

than it actually is. Output of du doesn’t 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.