Automatic space reclamation failure causes ESXi host to disable UNMAP processing
Article ID: 452634
Updated On:
Products
Issue/Introduction
- Automatic space reclamation on VMFS datastore (unmap) on Hitachi LUNs fails repeatedly.
- Subsequently, the /var/log/vmkernel.log indicates that the ESXi host has disabled UNMAP processing for the affected volume.
YYYY-MM-DDTHH:MM:SS.###Z Wa(###) vmkwarning: cpu#:#######)WARNING: Unmap6: ####: Removing unmap processing from volume <VOLUME_NAME> , as there are lot of Unmap IO errors observed
Environment
- VMware vSphere ESXi 8.x
- VMFS6 Datastores
- Hitachi VSP Storage
Cause
This issue is caused by a block alignment mismatch between the ESXi host and the storage array. During automatic space reclamation (UNMAP), the ESXi host attempts to process blocks using sizes or address boundaries that are incompatible with the storage array’s configuration.
These alignment conflicts result in the following vmkernel errors:
YYYY-MM-DDTHH:MM:SS.###Z In(###) vmkernel: cpu##:#######)ScsiFds: ###: Issue of delete blocks failed [sync:0] numDescs 1 Address is not aligned on required boundary 0x###########YYYY-MM-DDTHH:MM:SS.###Z In(###) vmkernel: cpu##:#######)ScsiFds: ###: Issue of delete blocks failed [sync:0] numDescs 1 Address is not aligned on required boundary 0x###########YYYY-MM-DDTHH:MM:SS.###Z In(###) vmkernel: cpu##:#######)ScsiFds: ###: Issue of delete blocks failed [sync:0] numDescs 1 Address is not aligned on required boundary 0x###########
When the storage array persistently rejects these requests, the resulting I/O errors ("Issue of delete blocks failed") trigger an ESXi protective mechanism. To maintain storage stability and prevent potential performance degradation, the host automatically disables UNMAP processing for the impacted datastore.
Resolution
To resolve this issue, ensure the storage array configuration is aligned with ESXi and VMFS6 requirements:
- Verify Storage Configuration: Coordinate with the storage vendor to ensure the 'Host Mode Options' (HMO) or 'Host Persona' are correctly configured for ESXi compatibility. For Hitachi VSP, specific HMOs are often required to support UNMAP correctly.
- Confirm Alignment Support: Verify that the array's block granularity settings do not conflict with the 1 MB alignment required by VMFS6 for automatic space reclamation.
- Re-enable UNMAP : Once the storage configuration is corrected, a host reboot or volume remount may be required to clear the "Removing unmap processing" state, though correcting the underlying alignment issue is the primary requirement.
Additional Information
Feedback
