Having a solid data backup plan is crucial for any business or individual who values their data. There are four main backup strategies that are commonly used: full backups, differential backups, incremental backups, and mirror backups. Understanding the key differences between these four approaches can help you determine the best backup method for your specific needs.
Full Backups
A full backup, also known as a complete backup, copies all the data files and folders you specify to the backup destination. This backup method captures everything at a specific point in time. Full backups take the longest time to complete compared to other backup types and also require more storage space.
Here are some key facts about full backups:
- Copies all specified data, programs, and operating system files
- Captures the entire data set at a single point in time
- Takes the longest time to complete
- Requires the most storage space
- Allows for a complete restore of a system
Full backups are sometimes referred to as baseline backups because they establish a baseline of your data at a point in time. All subsequent incremental or differential backups build off the full backup.
Pros:
- Allows for a complete restore of a system
- Simple backup and recovery process
- Minimal restore time needed
Cons:
- Slow backup speed
- Uses more storage space
- Captures redundant data each time
Full backups are recommended when first establishing a backup routine. After the initial full backup, incremental or differential backups are generally used in conjunction to minimize backup windows and storage requirements.
When to use full backups
- When establishing the first backup set
- For monthly or weekly backups
- When bandwidth impact is not a concern
- Required by compliance regulations
- For system or environment migrations
Incremental Backups
Incremental backups only capture data that has changed since the last full or incremental backup. After an initial full backup, incremental backups are generally scheduled more frequently to preserve data changes between full backups.
Key facts about incremental backups:
- Only backs up data changed since last backup
- Smaller backup sizes compared to full backups
- Faster backup times
- Requires access to other backup sets for restore
Incremental backups provide more frequent coverage but with less data copied each time. This saves storage space while also enabling more granular restore points.
Pros:
- Faster backup times
- Requires less storage space
- Allows for frequent backup schedules
Cons:
- No single backup set contains all data
- Requires more steps to restore data
- Old backup sets must be retained
Incremental backups strike a balance between backup frequency and required storage capacity. They enable more restore points compared to only using periodic full backups.
When to use incremental backups
- When full backups are too large or take too long
- For daily or frequent backups
- For databases or other frequently changing data
- To minimize bandwidth impact from backups
Differential Backups
Differential backups capture all data changed since the last full backup. This differs from incremental backups which only contain data changed since the last backup of any type. With differentials, the data captured continues to grow until the next full backup is performed.
Key facts about differential backups:
- Contains data changed since last full backup
- Faster restore process than incrementals
- Only needs the most recent differential and last full backup to restore
Differential backups provide a middle ground alternative. They avoid the longer restore times of incrementals while also minimizing redundant data copied over time.
Pros:
- Faster restore process
- Minimizes redundant data over time
- Provides multiple restore points
Cons:
- Larger backup size than incrementals
- Slower backup speed than incrementals
- Still requires periodic full backups
Differential backups work well for data that does not change extensively between full backups. They can provide a streamlined restore process with less overhead than incrementals.
When to use differential backups
- When full backup windows are too long
- For databases with some data churn
- For weekly or periodic backup schedules
- For data that changes moderately over time
Mirror Backups
Mirror backups, also known as clones or replication, involve maintaining a live copy of data sets on a separate storage system. This separate system maintains an identical image that mirrors the primary data set. Any changes to the primary data are immediately reflected in the mirror backup.
Key facts about mirror backups:
- Maintains a live, replicated copy of data
- Performs continuous replication of changes
- No backup schedule or windows required
- Allows immediate failover to mirror system
Mirroring provides real-time, continuous data protection and availability. Failover to the mirror can be almost instantaneous. But mirroring requires equivalent or greater storage capacity.
Pros:
- Real-time backup with no windows
- Allows immediate cutover or failover
- Maintains a continuously available backup
Cons:
- Requires separate storage at original capacity
- Heavier resource demands
- Higher infrastructure costs
Mirror backups provide the highest level of availability and the least downtime for restores. But the tradeoff is much higher storage, network and server infrastructure demands.
When to use mirror backups
- For mission-critical data that cannot have downtime
- To provide high availability and fast disaster recovery
- For real-time data replication
- Where backup windows are unacceptable
Comparing the Backup Strategies
Here is a comparison of some key attributes between the different backup strategies:
| Backup Type | Data Captured | Backup Speed | Required Storage | Restore Speed |
|---|---|---|---|---|
| Full | All specified data | Slow | High | Fast |
| Incremental | Data since last backup | Fast | Low | Slow |
| Differential | Data since last full | Moderate | Moderate | Moderate |
| Mirror | All data in real-time | Real-time | Very high | Very fast |
As seen in the comparison, each strategy has tradeoffs. Faster backup speed and more recovery points comes at the cost of slower restores and higher storage capacity with incremental backups. Differential backups provide a compromise on these factors. And mirror backups require investing in an equivalent secondary infrastructure to attain real-time availability.
How to Choose the Right Backup Strategy
Choosing the most appropriate backup strategy involves weighing factors such as:
- Restore requirements – How quickly must data be restored? What backup and recovery time objectives are acceptable?
- Change rate – How frequently does your data change? Does it require daily or real-time backups?
- Available storage – What is the storage budget for backups? Can disk targets meet retention policies?
- Backup windows – Are backups constrained to limited windows? Can backups run continuously?
- Compliance regulations – Are there regulatory or policy standards your backups must meet?
Considering these factors will guide the choice between approaches like incremental for low storage needs versus mirroring for constant uptime and fast failover requirements. Here are some general recommendations on which backup strategy works best for different situations:
- Full – For initial backup, monthly, or weekly schedules
- Incremental – For daily backups with limited storage and time
- Differential – For daily/weekly backups with moderate data changes
- Mirror – For constant uptime and instant failover needs
Organizations often utilize a combined approach with full, incremental and differential backup schedules. This provides layered coverage with full backups for broad restore needs, and incrementals or differentials for more granular daily changes.
Best Practices for Backup Strategies
Some best practices to follow for implementing backup strategies effectively include:
- Use disk targets for faster backup and recovery – Disk allows for faster backup speeds as well as restores.
- Retain multiple prior full backups – Keeping a rotation of the last 2-3 full backups protects against data corruption issues.
- Store backups offsite – Maintain offline, offsite backup copies for disaster recovery.
- Test restores regularly – Validate that backups are functioning properly with test restores.
- Document policies and procedures – Detail the backup process design and schedules for consistency.
- Automate backups when possible – Automating and centralizing backups improves reliability.
- Encrypt backups – Encryption protects backup data against unauthorized access.
- Monitor and get alerts on errors – Monitoring backup jobs and getting alerted on failures avoids blind spots.
Conclusion
The four main backup strategies each carry distinct advantages and disadvantages. Full backups provide maximum restore capabilities but with slow backup speeds. Incremental backups capture frequent changes fast but require more steps for recovery. Differential backups consolidate data changes from the last full backup for simpler restores. And mirror backups continuously replicate changes to maintain a live copy of data.
Factors like recovery time objectives, available storage and infrastructure, retention policies, and compliance requirements help determine which approach works best. Organizations often combine full, differential and incremental backup schedules for comprehensive data protection. Following backup best practices ensures your strategy operates reliably while meeting your specific data protection needs.
