Recommendations for creating a snapshot for a large virtual machine

Products

• VMware vSphere ESXi

Issue/Introduction

This article provides guidance on how snapshot size grows over time and where snapshot files are stored. 

Environment

vSphere ESXi 7.x

vSphere ESXi 8.x

Resolution

It is not possible to determine the exact size of a virtual machine snapshot before it is created. When a snapshot is taken, the delta (redo) log file is created with a minimal initial size. The snapshot grows over time based on the amount of data written, modified, or deleted on the virtual machine disks after the snapshot is taken.

Snapshot Behavior : 

• A snapshot captures a point-in-time state by generating a delta log file to record all subsequent changes to the base virtual disk (VMDK).
• Snapshot size increases incrementally as disk activity occurs after snapshot creation.
• The maximum size of a snapshot can approach the size of the base virtual disk.
• Virtual machines with high write workloads or large disks may experience accelerated snapshot growth.

Storage Planning : 

• Reserve 20%–30% additional free datastore capacity beyond the total virtual machine disk size to accommodate snapshot growth.
• Insufficient datastore space may lead to snapshot or virtual machine failures.

Snapshot Location : 

• For virtual machines with multiple disks on different datastores, a separate delta/redo log file is created for each disk.
• Snapshot files are always stored on the same datastore as their corresponding base disks.
• The snapshot file path is typically:
  /vmfs/volumes/<datastore>/<VM_name>/

Ensure that each datastore hosting any of the virtual machine’s disks has sufficient free space to support potential snapshot growth.

Additional Information

Snapshot Limitations