The three main types of backups are:

• Full Backup: Complete copy of all selected data regardless of when it was last backed up. Takes the most time and storage space but provides fastest recovery.
• Incremental Backup: Only backs up data that has changed since the last backup (full or incremental). Fastest backup time, least storage space, but slower recovery as you need the full backup plus all incremental backups.
• Differential Backup: Backs up all data changed since the last full backup. Moderate backup time and storage, faster recovery than incremental as you only need the full backup plus the latest differential.
  Example: If you do a full backup on Sunday, then:
• Monday incremental: backs up Monday's changes
• Tuesday incremental: backs up only Tuesday's changes
• Tuesday differential: backs up Monday + Tuesday changes

Backup retention refers to how long backup copies are kept before being deleted or overwritten. It's crucial for:

• Compliance Requirements: Many industries require data retention for specific periods (7 years for financial records)
• Point-in-Time Recovery: Ability to restore data from different time periods
• Storage Cost Management: Longer retention = higher storage costs
• Legal Protection: Historical data may be needed for litigation
  Common Retention Strategies:
• Daily backups kept for 30 days
• Weekly backups kept for 12 weeks
• Monthly backups kept for 12 months
• Yearly backups kept for 7 years

While often confused, backup and archive serve different purposes:
Backup:

• Creates copies of active data for recovery purposes
• Data remains in primary location
• Short to medium-term retention
• Focus on business continuity
  Archive:
• Moves infrequently accessed data to long-term storage
• Data is removed from primary location
• Long-term retention (years or decades)
• Focus on compliance and storage optimization
  Example: Email backup keeps copies of current emails for quick recovery, while email archiving moves old emails to cheaper storage for compliance purposes.

Recovery Time Objective (RTO):

• Maximum acceptable time to restore service after disruption
• Measured from disaster occurrence to full service restoration
  Recovery Point Objective (RPO):
• Maximum acceptable amount of data loss measured in time
• Last point in time to which data can be recovered
  Examples:
• E-commerce site: RTO = 2 hours (site must be online within 2 hours), RPO = 15 minutes (can lose max 15 minutes of orders)
• Email system: RTO = 4 hours, RPO = 1 hour
• Archived data: RTO = 3 days, RPO = 24 hours
  Key Point: Lower RTO/RPO requirements typically mean higher costs for backup and DR infrastructure.