See this page as a slide show
Chapter 10: Backups
Colorado State University
Computer Science Department
Original slides from Dr. James Walden at Northern Kentucky University.
- Backup policies and capacity planning
- Types of backups
- Backup media
- Backup security
- Accidental deletions
- Hardware failures
- Data corruption
- Natural disasters
- Security incidents
- Full (Archive) 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 of any type.
- Backup: fast, may store multiple per tape.
- Restore: slow, complex (requires multiple tapes)
- Differential backup
- Files changed since last full backup
- Backup: Needs more tape space than Incremental
- Restore: Only requires two tapes, at most, to restore all files.
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.
- 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 twenty-four hours.
- Data retention legal policies
- E-mail stored only for thirty days, for example.
- 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 differential backups.
- Assume 2GB of changes per day.
- Tape capacity needed:
- Day 1: 40GB
- Day 2: 2GB
- Day 3: 4GB
- Day 4: 6GB
- 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
- Transfer speed
- Flash Memory
- Very expensive, small media, personal use only.
- Super floppies
- ZIP 750MB, small capacity, high $/GB media.
- CD-R cheap drives, small (650MB).
- DVD-R cheap drives, but small (4.7GB)
- Hard disk
- Large capacity, bulky, fragile, low $/GB media.
- 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.
- 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.
- Linux defaults
- Open source
- Tivoli Storage Manager (IBM)
- Veritas Storage Manager
The key to efficiency and reliability!
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
- Tape security
- Tapes contain all of your important data.
- Data isn’t secure unless tapes are secure from accident or malice.
- 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?
- AIT, AIT Forum, http://www.aittape.com/index.html, 2006.
- Lynne Avery, “A Brief History of Tape,” Exabyte white paper,
- 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,
- Evi Nemeth et al, UNIX System Administration Handbook, 3rd edition,
Prentice Hall, 2001.
- 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,”
- “The Tao of Backup,” http://www.taobackup.com/
- Wikipedia Contributors, “Magnetic Tape,”
- Elizabeth Zwicky, “Torture Testing Backup and Archive Programs,”