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Chapter 10: Backups

Colorado State University

Computer Science Department

Original slides from Dr. James Walden at Northern Kentucky University.

Topics

1. Backup policies and capacity planning.
2. Types of backups.
3. Backup media
4. Automation
5. Backup security.

Why Backups?

• Accidental deletions.
• Hardware failures.
• Data corruption.
• Security incidents.

Backup Types

• Full backup
  • Complete copy of all files from a particular time.
  • Backup: slow, requires high capacity.
  • Restore: fast, simple.
• Incremental backup
  • Storage of changed files since last backup.
  • Backup: fast, may store multiple per tape.
  • Restore: slow, complex (requires multiple tapes)

Backup Policies

Backup requirements for organization.

• Explains reasons for backups.
• Explains what backups are.
• Indicates which data is backed up.
• Indicates frequency of backups.
• Provides backup Service Level Agreement (SLA).
• Defines legal data retention requirements.

SLA Parameters

• File restore time and granularity
  • How long to restore a file? Snapshots, tapes.
  • Daily to monthly granularity, depending on age.
• Disk failure restore time
  • How long to restore the disk? Hours, days.
  • How much data will be lost? Last 24 hours.
• Data retention legal policies
  • E-mail stored only for 30-days, for example.

Backup Schedule

• Determined by Policy and SLA.
• Schedule provides following information:
  • Which servers, partitions backed up?
  • How often are full backups performed?
  • How often are incrementals performed?
• Schedule determines capacity needs.

Capacity Planning: Space

• Partition: 40GB
  • Full backup every week.
  • Daily incremental backups.
  • 50% full now, grows 2GB per day
• Tape capacity needed
  • Day 1: 40GB
  • Day 2: 2GB
  • …
  • Day 7: 12GB
  • Day 8: 40GB

Capacity Planning: Time

• Fileserver: 4TB
• Full backup must finish overnight (8 hours)
• Tape drive: 40MB/s = 144 GB/hr = 1.15TB/night
• Need 4 tape drives running simultaneously.
• Additional concerns:
  • Network performance of file & backup servers.
  • Does any capacity need to be reserved for restores?
  • Actual performance vs. manufacturer specs.

Capacity Planning: Media

How much media do you need?

• Determined by policy and schedule.
• How long are full backups kept?
• How often are incrementals recycled?
• How often are tapes moved off-site?

Choosing a Backup Drive

1. Reliability
2. Transfer speed
3. Time-to-data
4. Capacity
5. Compatibility
6. Cost

Backup Media

• Flash Memory
  • Very expensive, small media, personal use only.
• Super floppies
  • ZIP 750MB, small capacity, high $/GB media.
• Optical
  • CD-R cheap drives, small (650MB).
  • DVD-R cheap drives, but small (4.7GB)
• Hard disk
  • Large capacity, bulky, fragile, low $/GB media.
• Tapes
  • Large capacity (500GB), low $/GB media; expensive drives.

Current Tape Formats

• LTO (Linear Tape Open)
  • Uses Ultrium format tapes.
  • LTO3: 400GB capacity, 35 MB/s, 49s seek
• Super DLT (Digital Linear Tape)
  • Backward compatible with DLT formats.
  • SDLT 600: 300GB capacity, 36 MB/s, 79s seek
• SuperAIT (Advanced Intelligent Tape)
  • SAIT-1: 500GB capacity, 30 MB/s, 45s seek

Common Tape Features

• Form Factor
  • 5.25″ FH SCSI drives
  • Media are ~½″ wide tape stored in cartridges.
• Hardware compression
  • Usually cited as 2:1, some cite higher.
  • Depends heavily on nature of data stored.
• Future Roadmaps
  • Plans to double capacity in next few years.

Tape Autochangers

• Stackers
  • Works sequentially through a stack of tapes.
• Autoloader / Jukebox
  • Provides random access to set of tapes.
• Library / Silo
  • Multiple drives with random access to set of tapes.
  • May incorporate bar code reader, ethernet, etc.

Backup Software

• Linux defaults
  • cpio, dump, rsync, tar
• Open source
  • AMANDA
  • Bacula
• Commercial
  • Tivoli Storage Manager (IBM)
  • Veritas Storage Manager

Automation

The key to efficiency and reliability

• Use cron instead of manually backing up
  • Single tapes require manual media change.
  • Tape libraries automate this process.
• Other automated tasks
  • Monitoring (up/down, disk space, security)
  • Logs (rotation, monitoring)
  • File distribution

Cron

• Performs tasks at scheduled times.
• Crontab files specify schedule of tasks
  • root: /etc/crontab
  • users: /var/spool/cron/crontabs/*
• Cron may log activities and errors.
• Timing limitations:
  • Runs tasks (if any) every minute.
  • Does not perform scheduled tasks if system down.
  • May or may not perform tasks on DST transition.

Crontab

Format: minute hour day month weekday user command

    30 4 * * 0 root yum -y update
     3 * * * * root (cd /var/www; make)
    20 1 * * * root /usr/local/rot-logs

“user”? Yes, /etc/crontab has a user field.

Managing Automated Tasks

• Divide by time: Hourly, daily, weekly, monthly tasks
• Crontab uses run-parts meta-script:

    17 * * * * root run-parts --report /etc/cron.hourly
    25 6 * * * root run-parts --report /etc/cron.daily
    47 6 * * 7 root run-parts --report /etc/cron.weekly
    52 6 1 * * root run-parts --report /etc/cron.monthly

• Add crons by placing script in time directory
• Add random delay if all hosts share same crontab

Backup Security

• Tape security
  • Tapes contain all of your important data.
  • Data isn’t secure unless tapes are secure.
  • Solutions: tape vault, encrypted tapes.
• Backup server security
  • Has read access to all important data.
  • If backup server isn’t secure, data isn’t secure.
  • Solutions: integrity checking, least privilege
• Restore process
  • Who can request files to be restored?
  • Where will restored file be placed?
  • What will its protections be?

References

• AIT, AIT Forum, http://www.aittape.com/index.html, 2006.
• Lynne Avery, “A Brief History of Tape,” Exabyte white paper, http://www.kontron.com/techlib/whitepapers/A_brief_history_of_tape.pdf, 2000.
• Aeleen Frisch, Essential System Administration, 3rd edition, O’Reilly, 2002.
• LTO, http://www.ltotechnology.com/newsite/index.html, 2006.
• Peter McGowan (ed), Quantum DLTape Handbook, http://downloads.quantum.com/sdlt320/handbook.pdf, 2001.
• Evi Nemeth et al, UNIX System Administration Handbook, 3rd edition, Prentice Hall, 2001.

More References

• Shelley Powers et. al., UNIX Power Tools, 3rd edition, O’Reilly, 2002.
• W. Curtis Preston, UNIX Backup & Recovery, O’Reilly, 1999.
• Quantum, “Tape Storage Automation,” http://www.dlt.com/storage/whitepapers/quantum/dlt/Tape%20Storage%20Automation.pdf
• “The Tao of Backup,” http://www.taobackup.com/
• Wikipedia Contributors, “Magnetic Tape,” http://en.wikipedia.org/wiki/Magnetic_tape, 2005.
• Elizabeth Zwicky, “Torture Testing Backup and Archive Programs,” ftp://ftp.berlios.de/pub/star/testscripts/zwicky/testdump.doc.html, 1991.