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I am experiencing a persistent failure when trying to back up an Azure File Share to a specific Recovery Services Vault (RSV). The failure occurs in the data transfer phase, and the recommended action to retry has not resolved the issue.
| Field | Value |
|---|---|
| Error Code | 850000 |
| Error Code | 850000 |
| Error Message | Failed to transfer data to vault |
| Data Transferred | 0.00 MB |
| Source | Azure File Share |
| Target | Recovery Services Vault |
| Failure Sub-task | Transfer data to vault |
| Success Sub-task | Take Snapshot (Completed) |
Take Snapshot sub-task completes successfully, confirming the source file share is healthy and accessible for snapshot creation.Job Duration: The failed job runs for nearly 2 hours (12:52:58 AM to 2:50:28 AM), suggesting it is timing out or waiting for a resource that never responds.
I have performed the following debugging steps without success:
Retried the Job: The operation was retried after waiting, but it failed again with the same error.
Networking Check: Verified the Storage Account Networking settings. The "Allow Azure services on the trusted services list to access this storage account" exception is enabled. The storage account is configured for Microsoft network routing.
IAM Permissions Check: Confirmed the failing Recovery Services Vault's Managed Identity has the necessary role (specifically, the Storage File Data Privileged Contributor role) assigned at the Storage Account level.
Resource Locks: Confirmed there are no resource locks (e.g., Read-Only) on the Storage Account that would prevent the vault from writing data.
Re-registration: I have Unregistered the Storage Account from the failing RSV, and then triggered a new backup job, forcing an implicit re-registration. The job still failed.
Given that a parallel backup is working and the snapshot is created, this appears to be a network or resource issue specific to the failing Recovery Services Vault or its internal connection path to the Storage Account. What specific advanced diagnostic checks can I run to identify why the data transfer is blocked at the 0.00 MB stage for this specific vault?I am experiencing a persistent failure when trying to back up an Azure File Share to a specific Recovery Services Vault (RSV). The failure occurs in the data transfer phase, and the recommended action to retry has not resolved the issue.
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Hello Ameera Haider
Thank you for posting your query on Microsoft Q&A platform.
The backup is failing at the “Transfer data to vault” stage with Error 850000, even though the “Take Snapshot” sub‑task completes successfully and you have validated IAM, networking, locks, and re‑registration. Since snapshots are generated directly at the storage layer, but vault transfer requires the Azure Backup service to enumerate and ingest data into the Recovery Services Vault, the failure indicates an issue between the storage account and the vault, not with the source file share itself.
Based on Microsoft official documentation, the following two checks are the most relevant and commonly responsible for cases where 0 MB is transferred despite a successful snapshot.
Microsoft officially documents that Azure Files vaulted backup supports a maximum of 10 million files per share. If the share exceeds this limit, snapshot creation still succeeds, but the Transfer to vault operation will fail or time out because the vault cannot enumerate metadata at scale.
Check the estimated file count in the share. If the total is >10 million, this is the root cause and the backup to vault is not supported. You will need to reduce the file count or split the namespace across multiple shares.
a. Storage Account and Vault must be in the same region: If they are in different regions, snapshot will work but data transfer will fail.
b. Storage Account can be protected by only one Recovery Services Vault: If the Storage Account is still registered to a different vault (even due to stale registration), the transfer stage fails at 0 MB.
c. Correct firewall settings for Backup ingestion: Storage Account firewall must allow “Allow Azure services on the trusted services list to access this storage account”, otherwise transfer to vault fails even when snapshots succeed.
You have already enabled the trusted services exception but ensure there are no private endpoints or network rules blocking Microsoft Backup service traffic.
Below details matches your symptoms:
This pattern aligns with the unsupported‑file‑count scenario and the documented vault-registration/region/network conditions.
Resolution Steps:
Verify file count and ensure the share contains ≤10 million files (Microsoft-supported limit).
If above limit → This is the root cause; Azure Files vaulted backup cannot proceed.
Confirm the storage account and the Recovery Services Vault are in the same region.
Use the Microsoft script (in the troubleshooting doc) to ensure the storage account is registered to only one vault.
Revalidate storage firewall rules strictly follow Microsoft guidance.
References: https://learn.microsoft.com/en-us/azure/backup/troubleshoot-azure-files
Thanks,
Suchitra.
Thank you for your response,
but the number of files is 11.02k so well below 10M.
The region is the same.
The storage account is not registered in any other vault.
The issue persists. Also note that the snapshot and vault transfer both were successful in the first two backup jobs, it started failing afterwards.
Hello Ameera Haider
Thank you for confirming the details.
Since File count is ~11K (well below the 10M limit), storage Account and Vault are in the same region, storage Account is not registered to any other vault and the first two backup jobs succeeded, and failures started afterward, the issue is not related to supported limits or region mismatches.
when “Take Snapshot” succeeds but “Transfer data to vault” fails, the failure is caused by vault-side ingestion issues, transient vault pipeline throttling, or storage firewall/network path restrictions, not by source data or file count.
Even minor changes in firewall/PE settings can cause transfer failures after previously working jobs.
Enable Azure Backup Diagnostics to Identify Exact Vault Failure Reason: When transfer-to-vault fails repeatedly with Error 850000, it is recommended enabling Backup diagnostics to view:
These logs reveal:
Re‑register the Storage Account Using PowerShell (Not Portal Only): If storage account registration becomes stale or partially corrupted, transfer-to-vault failures can occur even though snapshots succeed.
Thanks,
Suchitra.