I/O Delay During FSTRIM Execution on VPS

Status: Resolved
Severity: Low
Category: Performance
First Observed: February 2026
Resolved: June 2026
Affected Services: Limited number of VPS instances using specific hardware emulation profiles (NVMe and HDD RAID tiers)

Summary

Following the upgrade to Proxmox VE 9.1, isolated reports indicated that execution of fstrim within a VPS could, under specific circumstances, result in a temporary increase in I/O wait on the underlying storage subsystem.

Subsequent investigation identified the behavior as being associated with a particular virtual machine hardware emulation profile rather than the storage platform itself.

Impact

• Temporary increase in I/O wait during trim operations (typically observed in the ~20–25% range)

• Short-lived performance fluctuation while the discard operation was in progress

• No data integrity issues were identified

• No persistent storage performance degradation was observed

Customer Impact

• Only a limited number of VPS instances were affected

• Performance impact was limited to the duration of the trim operation

• No customer data was at risk

• No customer intervention was required

Root Cause

Engineering analysis determined that the behavior was limited to virtual machines configured with the Q35 machine type (hardware emulation profile).

The issue could not be reproduced on alternative machine types under equivalent workloads, confirming that the storage infrastructure itself was operating normally.

Resolution

HOST-C completed the evaluation of available mitigation options and implemented the appropriate hardware emulation profile for affected virtual machines.

Following the change:

• FSTRIM operations complete normally

• The elevated I/O wait condition is no longer observed

• No customer workload migration or manual intervention was required

• Platform performance has returned to expected operating parameters

Post-remediation monitoring has confirmed stable storage behavior across all affected infrastructure.

Closing Statement

The issue has been fully resolved.

The observed behavior was limited in scope, presented no risk to customer data, and was successfully mitigated through platform configuration improvements. Continuous monitoring confirms normal storage performance across the HOST-C virtualization platform.

HOST-C Network
"Storage by Design"