Problem Description:
Understanding Disk Usage Discrepancies in CloudRanger Backup Reports
This article outlines our findings and explains the cause behind these differences, particularly when backing up Windows-based resources.
Observations
The credit consumption reports for backups to Druva Cloud (Windows resources) does not align with the actual disk usage on their virtual machines (VMs). Below is a summary of the reported discrepancies:
Disk Usage Discrepancies
Resource 1
AWS Volume Size: 1000 GB
Reported Usage: 649.13 GB
Actual VM Usage: 170 GB used / 830 GB free
Resource 2
AWS Volume Size: 1500 GB
Reported Usage: 823.59 GB
Actual VM Usage: ~240 GB used (1.22 TB free out of 1.46 TB)
Resource 3
AWS Volume Size: 4120 GB
Reported Usage: 4119.94 GB
Actual VM Usage:
C Drive: 120 GB total / 32.9 GB free
D Drive: 3.90 TB total / 183 GB free
Findings:
The disk usage reported in CloudRanger is based on AWS snapshot sizes, not the real-time used space visible from inside the VMs.
Snapshot data can we reviewed and validated directly from the AWS Console.
The reported values in CloudRanger matched the AWS snapshot sizes exactly.
For instance, one Windows and one Linux—with identical 30 GB storage volumes: Windows Snapshot Size: 28.65 GB , Linux Snapshot Size: 1.68 GB
Conclusion:
Windows OS tends to write small amounts of data across many blocks, which leads to increased snapshot sizes.
AWS snapshots operate at a 512 KB block level, meaning any written block (regardless of actual data size) is fully captured.
This behaviour significantly inflates snapshot size on Windows systems, resulting in higher reported usage in backup and credit reports.