AOMEI Cyber Backup
How to Solve Large Backup File of Almost Empty VM
Large backup files of almost empty VMs may seem like a minor inconvenience, but they can wreak havoc on system performance, cost efficiency, and disaster recovery operations. Therefore, resolving this issue can maintain the health of the virtual environment.
By Amelia / Updated on April 11, 2025
One of the challenges you may encounter when working with virtual machines (VMs) is dealing with large backup files, especially when the VM is almost empty. This can be confusing when encountered because the VM does not contain important data or workloads, yet its backup files are unexpectedly large. In this article, you will be provided with the reasons for the large size of the backup file for an almost empty VM and solutions to reduce the backup size for empty VMs.
Why Is Backup File So Large for an Almost Empty VM
1. Disk Space Allocation (Thick Provisioning)
A certain amount of virtual disk space is typically allocated to a virtual machine when it is created, even if the virtual machine does not use all the space. In many cases, a thick configuration is used where the entire disk space is pre-allocated.
2. VM Snapshot and Delta Files
Snapshots store changes made after the snapshot occurs in delta files, which accumulate over time, increasing backup size.
3. Virtual Machine Configuration Files
When backing up a virtual machine, what is captured is the data on the virtual disk as well as the virtual machine configuration file (such as .vmx or .vbox). Although they are usually small, they also increase the size of the backup file.
Solutions to Reduce Backup Size for Empty VM
The following parts offer several solutions to backup file so large for an almost empty VM.
1. Using Thin Provisioning
When creating virtual disks, you can use thin provisioning, which allocates space only when writing data, which means that thin provisioning can significantly reduce the size of backups.
2. Deleting Unused Snapshots
Multiple snapshots of a virtual machine can significantly increase the size of the backup. So, snapshots need to be managed, merged, or deleted regularly to prevent unnecessary accumulation of delta files.
3. Zeroing out Free Space
Tools can be used to zero out free space or shrink virtual disks before making a backup of a virtual machine. This removes residual data from unused disk sectors and reduces the size of the backup.
4. Optimizing Storage Usage for Virtual Machines
Regularly cleaning up the virtual machine's file system, removing unnecessary files, and running disk cleanup utilities to ensure that there are no orphaned files or redundant data on the virtual disk helps reduce the amount of data that needs to be backed up.
5. Snapshot Consolidation
If virtual machines have a long history of snapshots, you can consider de-consolidating them, which helps simplify the virtual disk structure and reduce the backup size.
Using Incremental or Differential Backup to Reduce Backup Size
To improve the case of large backup file almost empty VM, you can use incremental or differential backups to reduce the size of the backup file. AOMEI Cyber Backup can provide you with such an option, and it offers the following features:
- It provides a centralized backup solution, which allows you to back up VMs, systems, disks, and partitions flexibly.
- It simplifies the backup process by allowing you to perform an initial full backup followed by an incremental or differential backup, ensuring that only modified or newly added data is saved, which saves storage space and speeds up the backup process.
- It allows you to easily schedule backups, manage multiple backup tasks, and restore data efficiently, ensuring valuable files are always protected.
- It provides a user-friendly interface and robust features, making it perfect for both personal and professional use.
Follow simple steps to configure incremental backup
Step 1. Install and open the AOMEI Cyber Backup, navigate to Source Device > VMware > Add VMware Device to add vCenter or Standalone ESXi host as the source device.
Step 2. In Backup Task, click Create New Task to set to backup.
- Task Name: Enter a backup task name.
- Backup Type: You can choose VMware ESXi Backup or Hyper-V Backup.
- Device Name: Select the device and virtual machines you want to back up and click OK.
- Target: Choose a location to store your backup files. You can choose a local or a network path. Click OK.
- Schedule: Click Enable Schedule to start scheduling backup tasks. In the Backup Method, you can choose Full Backup, Incremental Backup, and Differential Backup. In Schedule Type, you can specify the backup time, such as daily, weekly, monthly (by week), or monthly (by data).
Step 3. After all these configurations, click Start Backup to start the backup process.
📌While the Free Edition can meet most of your VM backup needs, you can also upgrade to enjoy:
Batch VM Backup: Batch backup large numbers of VMs managed by vCenter Server or Standalone ESXi hosts.
Backup Cleanup: Configure a retention policy to auto-delete old backup files and save storage space.
Restore to new location: Create a new VM in the same or another datastore/host directly from the backup, which saves the trouble of reconfiguring the new VM.
Conclusion
Disk configuration choices, snapshot management issues, and inefficient backup processes often result in large backup files of almost empty VMs. In this article, we provide you with some ways to help reduce the size of VM backups and improve storage efficiency and backup speed.
