Failed to transfer data to vault : SMB FILE SHARE

LARIBI Ahlem 0 Reputation points

Hello;

The daily backup of our SMB file share has been failing consistently for over 30 days. Each night, the backup runs for approximately 10 to 12 hours before failing with error code 850000 – "Failed to transfer data to vault".

I have investigated the issue and applied some solutions, including adjusting the backup start time to avoid overlap with VM backups. I have also checked and ruled out the following potential causes:

  • Storage account firewall / Trusted services exception: "Allow Azure services on the trusted services list to access this storage account" is enabled, with Microsoft.RecoveryServices/vaults explicitly allowed as a resource.
  • Shared key access: Enabled.
  • SAS policy: No restrictions configured.
  • Resource locks: Only the expected CanNotDelete lock is present.
  • the storage account and the Vault are in the same region
  • File count in the share is 500K.

Error Details :

  • Region: France Central
  • File Count in the share: avg 500k > 10 million
  • Failed job ID (example): efd81308-bfa8-4384-abc1-352d10b0b540
  • Error code: 850000
  • Data Transferred (in MB): 36940.03 ==! 0
  • Pattern: Fails every night after 10+ hours of transfer; all VM backups in the same vault complete successfully The daily backup of smb file share has been failing consistently for over 30days. Each night, the backup runs for approximately 10 to 12 hours (transferred data ==! 0) before failing with error code 850000 – "Failed to transfer data to vault".

Regards,

  1. Suchitra Suregaunkar 14,595 Reputation points • Microsoft External Staff • Moderator

    Hello @LARIBI Ahlem

    Thank you for posting your query on Microsoft Q&A platform.

    We are looking into this issue and will keep you posted updates.

    Thanks,

    Suchitra.

  2. Suchitra Suregaunkar 14,595 Reputation points • Microsoft External Staff • Moderator

    Hello @LARIBI Ahlem

    As per the official Azure Files backup support matrix, the Vault-standard tier has a documented hard limit:

    👁 User's image

    If the file count exceeds 10 million, the backup will fail during the "Transfer data to vault" phase which is exactly what is happening here.

    Could you please share us the below details?

    Could you please confirm the exact total number of files and directories in the file share? You mentioned "avg 500k > 10 million" — does the file share currently contain more than 10 million files/directories?

    You can check this from:

    • Azure Portal → Storage Account → File Shares → Properties (shows approximate file count)

    Your description says "avg 500k > 10 million", could you please clarify:

    • Is the total file count currently above 10 million?
    • Or does it fluctuate between 500K and 10 million?
    • Has the file count grown recently (e.g., due to data migration or application activity)?
    1. Backup tier confirmation: Are you using the Vault-standard tier (vaulted backup) or Snapshot-only tier for this file share backup? This is important because the file count limits differ between the two tiers.
    2. Did this backup work successfully in the past? If yes, approximately when did it start failing, and were there any changes around that time (e.g., data growth, file migration)?
    3. Is this a single file share with all the files, or are there multiple file shares under the same storage account? If multiple, what is the file count per share?

    This information will help us confirm whether the failure is caused by exceeding the documented file count limit.

    Reference: Support matrix for Azure Files backup

    Thanks,

    Suchitra.

  3. Suchitra Suregaunkar 14,595 Reputation points • Microsoft External Staff • Moderator

    Hello @LARIBI Ahlem

    Just checking in to see if the solution shared above help you to resolve your issue. please reach out to us If you have any further questions.

    Thanks,

    Suchitra.

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1 answer

  1. LARIBI Ahlem 0 Reputation points

    Please also note that the backup was working before on the same vault.

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