Chapter 11 Backups

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 quality Drive Model Tape Length Capacity 8200 8500 8505 8505XL 112 112 112 160 8900 (Mammoth) 170 5 7 2.3Gb

5 20

Sometimes Smaller Is Better

 4mm • Based on DAT (Digital Audio Tape) format Tape Format DDS-1 DDS-DC DDS-2 DDS-3 Tape Length 60 90 120 125 2 4 Capacity 1.3GB

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 DLT 4000 DLT 7000 DLT 8000 Capacity 20GB 35GB 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.