File Upload to vSAN Datastore Fails with "Failed to transfer data"
Article ID: 447277
Updated On:
Products
Issue/Introduction
When attempting to upload files (ISO, OVF, etc.) to a folder on a vSAN datastore, the operation fails with the following symptoms:
- The error "Failed to transfer data" or "Operation failed for an undetermined reason" appears in the vSphere Client.
- Uploads to local datastores work without issue.
- Browser CA certificates are correctly installed and trusted.
- The issue persists when uploading directly via the ESXi Host Client or the vCenter UI.
Environment
VMware vSAN (all versions)
Cause
Folders created directly on a vSAN datastore are provisioned as vSAN Namespace Objects, which possess a hard capacity limit of 255 GB. Once this limit is reached, the namespace objects block further write operations, causing file uploads to fail.
Even if files inside the folder were previously deleted to free up space, vSAN does not automatically issue UNMAP/TRIM commands to reclaim space on namespace objects (it only reclaims unmapped space from standard Virtual Disks). As a result, deleted data acts as "ghost" blocks, leaving the namespace permanently marked as full.
Resolution
To resolve the issue and upload the files successfully, implement the following steps:
- If empty, delete the old folder entirely from the datastore browser to permanently destroy the exhausted namespace object and get space reclaimed.
- Create a brand new folder in its place, which provisions a fresh, empty vSAN namespace object with a clean 255 GB allocation.
- Proceed with the file upload into the newly created folder.
Additional Information
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