A Citrix VDI environment hosted on Nutanix AHV experienced a significant and unexpected increase in disk usage after deploying additional VDIs.

Windows includes an automatic maintenance process called Storage Optimizer (Defrag / Slab Consolidation), which periodically optimizes disk layout and consolidates data blocks.
When this process runs inside a Citrix MCS-provisioned VDI hosted on Nutanix AHV, it triggers extensive rewrite I/O operations at the guest level.

Because Nutanix uses thin-provisioned Copy-on-Write (CoW) virtual disks, each rewrite causes new physical blocks to be allocated on the storage layer instead of reusing existing ones.

As a result:

• Physical disk files expand rapidly

• Deduplication and compression efficiency decrease

• Overall storage consumption increases even though the logical data inside the guest OS remains largely unchanged

This is normal Windows behavior but is not recommended in HCI environments such as Nutanix AHV.

Disable the Windows Defrag (Storage Optimizer) feature in the master image before provisioning VDIs.

1. Disable Disk Defragmentation Boot Optimization

2. Disable Scheduled Disk Defragmentation Task

Open Task Scheduler →
Microsoft > Windows > Defrag > ScheduledDefrag
→ Right-click and Disable,
or execute the following command:

After disabling these settings, perform an MCS image update to apply the changes across all VDIs.

Unexpected Disk Space Increase on Nutanix AHV After Deploying Citrix VDIs.

Introduced in AOS 5.18, the Recycle Bin feature is enabled by default and holds deleted VM files for 24 hours to allow recovery.

During MCS machine catalog updates, old VDI disks are deleted and moved to the Recycle Bin. This can significantly increase disk usage and contribute to storage exhaustion.

Recommendation: Disable the Recycle Bin feature to prevent disk usage issues.
For more information, see: Disabling Recycle Bin in Prism Web Console