When it comes to data protection, few topics generate as much confusion as snapshot backup. The term “snapshot” means different things depending on whether you’re talking about traditional storage arrays or cloud platforms, and understanding these differences is critical for building effective backup strategies.
This blog post summarizes the main points of my latest podcast episode. If you’d like, you can listen to it or watch it at https://www.backupwrapup.com/
What Makes Snapshot Backup Different from Traditional Backups
A snapshot represents a view of your storage at a specific point in time. Think of it like taking a photograph – you capture exactly how things looked at that moment. But here’s where it gets interesting: the actual blocks you’re accessing when you look at that snapshot might come from different places depending on how the snapshot system works.
Traditional snapshots are read-only by design. You can’t modify a snapshot any more than you can change a photograph after it’s taken. This read-only nature is fundamental to what makes a snapshot useful for backup purposes.
The key thing to understand about traditional snapshot backup systems is that they depend on the original storage device remaining functional. The snapshot itself isn’t a complete copy – it’s more like a reference system that knows where to find the right version of each block of data.
Traditional Snapshot Backup Methods: Copy-on-Write vs Redirect-on-Write
There are two primary approaches to implementing snapshot backup in traditional storage systems, and the performance differences are dramatic.
Copy-on-Write Snapshots
The older approach, copy-on-write, works by copying the original block to a snapshot area before writing new data. This means every write operation actually requires three I/O operations: read the original block, copy it to the snapshot area, then write the new data.
The performance impact is severe. I’ve seen cases where organizations wanted 90 days of user-browsable snapshots but were told by their storage vendor that they’d experience a 50% performance degradation. The vendor actually said “no one does that with our storage” because the copy-on-write approach simply can’t handle long-term snapshot retention at scale.
Redirect-on-Write Snapshots
NetApp revolutionized snapshot backup with their redirect-on-write approach. Instead of overwriting blocks in place, new data gets written to available space elsewhere on the storage system. The snapshot system just keeps track of where everything is located.
This approach can handle thousands of snapshots with minimal performance impact, as long as you have enough storage space. NetApp systems can maintain up to 1,000 snapshots per volume, compared to the old limit of 255, because redirect-on-write doesn’t create the same I/O bottlenecks.
Cloud-Based Snapshot Backup: When Snapshots Become Real Backups
Here’s where things get confusing: cloud providers like AWS use the term “snapshot” to describe something completely different. When you take an EBS snapshot or an RDS snapshot, you’re not creating a storage view – you’re creating a full copy of your data that gets stored in object storage like S3.
These cloud snapshots are actually much closer to traditional backups. They create bite-for-bite copies that can be moved between regions, stored in different accounts, and managed independently of the original storage system. This means cloud snapshot backup can actually follow the 3-2-1 rule more easily than traditional storage snapshots.
Converting Snapshots into Real Backup Protection
Traditional snapshots alone don’t constitute proper backups because they violate the fundamental principles of the 3-2-1 rule. Here’s how to turn your snapshot backup into real data protection:
Copy to Different Storage Systems
The most important step is copying your snapshots to different storage platforms. This gives you protection against storage system failures and provides the “different media types” requirement of proper backup strategy.
Geographic Distribution
Copy snapshots to different locations. Even if you’re using the same vendor, having copies in different data centers provides protection against site-level disasters.
Immutable Storage Integration
Modern snapshot backup strategies should include immutable storage options. This means creating copies that even you can’t delete, providing protection against ransomware and rogue administrator scenarios.
Performance Considerations for Snapshot Backup Systems
The performance impact of your snapshot backup strategy depends heavily on the underlying technology. Copy-on-write systems become slower as you add more snapshots and keep them longer. Redirect-on-write systems maintain performance as long as you have adequate storage space.
Flash storage has made redirect-on-write even more attractive because it avoids the write amplification issues that can reduce SSD lifespan. Each flash memory cell has a limited number of write cycles, so minimizing unnecessary writes helps extend hardware life.
Best Practices for Enterprise Snapshot Backup
Understand Your Technology
Know whether your storage system uses copy-on-write or redirect-on-write. This determines how many snapshots you can reasonably maintain and how long you can keep them.
Plan for Growth
Redirect-on-write systems need adequate free space to handle snapshot data. Plan your capacity accordingly, especially if you want to maintain long-term snapshot retention.
Integrate with Backup Systems
Many backup applications can leverage storage snapshots to create consistent point-in-time copies without impacting production systems. This is particularly important for database backups and virtual machine protection.
Test Recovery Procedures
Whether you’re using traditional storage snapshots or cloud-based approaches, regularly test your ability to restore from snapshots. Make sure your recovery procedures work and that your team knows how to execute them.
The world of snapshot backup continues to evolve, but the fundamental principles remain the same: understand your technology, plan for performance impact, and make sure your snapshots become real backups through proper copying and distribution strategies.
Written by W. Curtis Preston (@wcpreston), four-time O'Reilly author, and host of The Backup Wrap-up podcast. I am now the Technology Evangelist at S2|DATA, which helps companies manage their legacy data
