Transcript Chapter 11 Backups Unix System Administration
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
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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
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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.