Snapshot Management Best Practices: When and How to Use VM Snapshots

VM snapshots are one of the most misunderstood features in virtualization. They’re incredibly useful for certain scenarios, yet they’re also one of the most common sources of performance problems and storage issues in virtual environments. The key to using snapshots effectively is understanding exactly what they are, what they’re not, and when they’re the right tool for the job.

What Snapshots Actually Are

A snapshot captures the state of a virtual machine at a specific point in time. When you create a snapshot, the hypervisor preserves the current state of the VM’s virtual disks and, optionally, its memory and power state. From that moment forward, all changes to the VM’s disks are written to a separate delta file rather than the original virtual disk.

This is crucial to understand: snapshots don’t create a full copy of your VM. Instead, they create a new file that stores only the changes made after the snapshot was taken. The original virtual disk becomes read-only, and the VM reads from it while writing all new data to the delta file. When you delete the snapshot, the hypervisor merges those changes back into the original disk.

This architecture makes snapshots quick to create—you’re not copying gigabytes of data—but it also means snapshots aren’t a backup solution. The original disk and the delta file are interdependent. If either becomes corrupted, your VM is at risk.

When to Use Snapshots

Snapshots excel in specific scenarios where you need a quick rollback point. Before applying patches or updates is perhaps the most common and appropriate use. You’re about to patch an operating system or update critical application software. Taking a snapshot gives you a safety net—if something goes wrong, you can revert to the pre-patch state in minutes rather than hours of restoration from backup.

Testing configuration changes is another ideal scenario. You need to modify database settings, change network configurations, or adjust application parameters, but you’re not entirely certain of the impact. A snapshot lets you experiment with confidence, knowing you can undo everything if needed.

Development and testing environments benefit significantly from snapshots. Developers can create a snapshot of their clean environment, make changes, test their code, then revert back to start fresh. This workflow is far more efficient than rebuilding VMs repeatedly.

Short-term protection during risky operations makes sense. You’re migrating data, performing a complex multi-step configuration, or doing maintenance that could potentially cause issues. A snapshot provides immediate rollback capability during that critical window.

When NOT to Use Snapshots

Understanding when to avoid snapshots is equally important. Snapshots are not backups. They live on the same storage as the VM itself. If that storage fails, both your VM and its snapshots are gone. Backups should always be your primary data protection strategy, stored on separate infrastructure.

Don’t use snapshots for long-term retention. Every snapshot creates performance overhead. The longer a snapshot exists, the larger its delta file grows, and the more performance degrades. Snapshots that persist for weeks or months can cause serious performance problems and create risk during the eventual consolidation process.

Avoid snapshots on high-transaction databases whenever possible. Database servers with constant write activity generate huge delta files rapidly. This not only impacts performance but makes the eventual snapshot deletion a lengthy, resource-intensive operation. If you must snapshot a database VM, keep the snapshot window as short as possible—ideally just hours, not days.

Don’t snapshot VMs with applications that maintain their own snapshots or consistency mechanisms. Some applications, particularly certain databases and email systems, have their own internal snapshot capabilities. Stacking VM-level snapshots on top of application-level snapshots can create consistency issues and complexity.

Production VMs shouldn’t carry snapshots indefinitely. If you find yourself keeping snapshots on production systems for days or weeks “just in case,” you’re using the wrong tool. That’s what backup solutions are designed for.

How Snapshots Impact Performance

Understanding performance implications helps you use snapshots more effectively. When a snapshot exists, every write operation requires additional work. The hypervisor must maintain the chain of delta files and track which blocks are in which file. This adds latency to write operations—typically small, but measurable.

As the delta file grows, performance degrades further. A VM with a 50GB delta file performs noticeably worse than one without snapshots. The hypervisor must search through the snapshot chain to locate data, and this overhead increases with each additional snapshot in the chain.

Storage capacity is another consideration. A busy VM can generate gigabytes of changes per day. That 100GB VM you snapshotted might consume 150GB or 200GB of storage after a few days with the snapshot active. Always ensure you have adequate free space before creating snapshots, typically at least 25-30% of the VM’s total disk capacity as a buffer.

Read operations are also affected, though less dramatically than writes. The hypervisor must check the delta file first for any changed blocks before reading from the original disk. With multiple snapshots in a chain, this lookup process becomes increasingly expensive.

Snapshot Best Practices

Successful snapshot management requires discipline and process. Always document why you’re creating a snapshot and when you plan to delete it. Many organizations implement automated alerts for snapshots older than 24 or 72 hours. This prevents the common problem of forgotten snapshots accumulating on systems.

Limit snapshot chains to one or two levels. Some administrators create snapshots of snapshots, building chains of three, four, or more levels. This exponentially increases performance overhead and creates risk during consolidation. If you need multiple recovery points, use proper backup solutions instead.

Take snapshots with memory only when necessary. Memory snapshots capture the VM’s active memory state, allowing you to return to exactly where the VM was—including running applications and open files. This is useful for testing scenarios where you want to return to a specific application state, but it adds time to snapshot creation and deletion. For most patching scenarios, disk-only snapshots are sufficient.

Avoid snapshotting VMs with independent disks. Some virtual disks can be configured as independent, meaning they’re excluded from snapshots. Having a mix of snapshotted and non-snapshotted disks on the same VM can create consistency issues.

Schedule snapshot creation during maintenance windows when possible. While creating a snapshot is relatively quick, there’s a brief moment when the VM pauses while the hypervisor sets up the delta file structure. For most workloads this pause is imperceptible, but latency-sensitive applications might notice.

Managing Snapshot Deletion

Deleting snapshots requires as much care as creating them. The deletion process—often called consolidation or committing—merges the delta file back into the original virtual disk. For large delta files, this operation can take considerable time and I/O resources.

Never delete multiple snapshots simultaneously on the same datastore. If you have several VMs with old snapshots that need cleaning up, delete them one at a time. Concurrent consolidations can saturate storage I/O and impact other VMs.

Schedule snapshot deletions during low-usage periods. The consolidation process is I/O intensive. Running it during business hours on production systems can cause noticeable performance degradation. Plan deletions for evenings or weekends when possible.

Monitor consolidation progress. Most hypervisors provide task progress for snapshot deletion. Very large snapshots (hundreds of gigabytes) can take hours to consolidate. Ensure you have adequate time before starting the operation.

Don’t forcibly cancel snapshot deletion unless absolutely necessary. If you interrupt the consolidation process, you can leave the VM in an inconsistent state requiring manual intervention to fix. Let the operation complete even if it takes longer than expected.

Platform-Specific Considerations

VMware vSphere creates snapshots using a delta disk mechanism with VMDK files. You can have up to 32 snapshots in a chain, though you should never approach this limit. VMware’s Snapshot Manager provides a tree view of snapshot relationships, making it easier to understand which snapshots depend on others. vSphere also includes snapshot consolidation warnings that alert administrators to potential issues.

Hyper-V uses a different approach with AVHD or AVHDX files depending on the version. Hyper-V’s implementation is generally more automated—for instance, checkpoint deletion happens automatically in the background. However, the same fundamental limitations apply: snapshots aren’t backups, and long-lived snapshots cause performance problems.

KVM-based systems typically use qcow2 internal snapshots or create new qcow2 files as external snapshots. The qcow2 format is specifically designed to support efficient snapshots, but it’s still subject to performance overhead with large or multiple snapshots. Tools like libvirt provide snapshot management capabilities, though the implementations vary across different management platforms.

Monitoring and Maintenance

Proactive monitoring prevents snapshot-related problems. Implement alerts for snapshots older than your defined threshold—typically 24-72 hours depending on your environment. Most virtualization platforms provide APIs or command-line tools to query snapshot age and size across your entire infrastructure.

Regularly audit your environment for forgotten snapshots. Even with alerts, snapshots slip through occasionally. Weekly or monthly reviews help catch stragglers before they cause serious problems.

Monitor storage capacity closely in environments that use snapshots frequently. Unexpected storage exhaustion is one of the most common snapshot-related issues. Ensure monitoring systems alert well before storage reaches capacity—ideally at 75-80% full.

Track snapshot deletion success rates. Failed consolidations require manual attention and indicate potential problems with storage performance or capacity. Regular failures might suggest you need to adjust your snapshot practices or upgrade storage infrastructure.

Alternatives to Consider

For many scenarios where snapshots seem appealing, better alternatives exist. Application-consistent backups with quick restore capabilities provide similar rollback functionality without the performance overhead of persistent snapshots. Modern backup solutions can restore VMs in minutes, often matching snapshot revert times.

Cloning creates a full, independent copy of a VM. While this requires more storage and takes longer than a snapshot, the clone is completely independent. This is ideal for creating test environments based on production systems.

Replication creates synchronized copies of VMs on separate infrastructure. This provides disaster recovery capabilities and, in some cases, the ability to boot from the replica if issues occur with the primary VM.

Application-level backup and recovery mechanisms, particularly for databases, often provide more granular recovery options than VM-level snapshots. SQL Server, Oracle, PostgreSQL, and other databases have robust backup capabilities that work better for database workloads than hypervisor snapshots.

Infrastructure as code and configuration management allow you to rebuild VMs from scratch quickly and consistently. For systems that can be redeployed rather than restored, this approach eliminates the need for snapshots entirely.

The Bottom Line

Snapshots are powerful tools when used appropriately but dangerous when misused. They excel at providing short-term rollback capabilities for patching, testing, and risky operations. They fail as backup solutions, long-term retention mechanisms, or set-and-forget safety nets.

Treat snapshots as temporary constructs with defined lifespans. Create them with purpose, monitor them actively, and delete them promptly. With discipline and proper procedures, snapshots become valuable additions to your operational toolkit rather than sources of performance problems and late-night emergencies.

The best snapshot management practices start with a simple question: Is a snapshot really the right tool for what I’m trying to accomplish? Often the answer is yes, but sometimes it’s not—and recognizing that difference makes all the difference in maintaining a healthy, high-performing virtual infrastructure.