How to fix Error 3238 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: SQL Server Error 3238 — Backup Size Exceeds Maximum Allowed File Size on Remote Endpoint

Why This Error Happens

This error occurs when SQL Server calculates an estimated backup size that surpasses the maximum file size limit imposed by the remote storage endpoint, such as Azure Blob Storage (page blob limit of 1 TB) or a block blob configuration with restrictive size caps. It typically arises when backing up large databases directly to a URL without striping the backup across multiple files or blobs. Additionally, outdated SQL Server backup-to-URL configurations or incorrect blob type selection (page blob vs. block blob) can trigger this miscalculation and enforcement failure.

Step-by-Step Resolution Guide

Step 1: Verify the Current Backup Target and Blob Type

  • Check whether the backup is being directed to a Page Blob or Block Blob on Azure Storage.
  • Page Blobs have a hard limit of 1 TB per file, while Block Blobs support striping and can scale up to 195 TB total when split correctly.
  • Run the following to inspect your backup command:
BACKUP DATABASE [YourDatabase] TO URL = 'https://yourstorageaccount.blob.core.windows.net/container/backupfile.bak'
  • Confirm the storage account type in the Azure Portal under Storage Account > Configuration > Account Kind.

Step 2: Implement Backup Striping Across Multiple URLs

  • Split the backup into multiple smaller files (striped backup) so no single file exceeds the remote endpoint’s limit.
  • Use multiple URL targets in a single BACKUP statement:
BACKUP DATABASE [YourDatabase]
TO URL = 'https://yourstorageaccount.blob.core.windows.net/container/backup1.bak',
   URL = 'https://yourstorageaccount.blob.core.windows.net/container/backup2.bak',
   URL = 'https://yourstorageaccount.blob.core.windows.net/container/backup3.bak'
WITH COMPRESSION, STATS = 10;
  • Ensure the number of files is sufficient to keep each stripe under the 1 TB (Page Blob) threshold.

Step 3: Switch to Block Blob Storage and Enable Compression

  • If using Page Blobs, migrate your backup credential and container configuration to support Block Blob storage, which handles large striped backups more efficiently.
  • Update the SQL Server credential used for the backup:
CREATE CREDENTIAL [https://yourstorageaccount.blob.core.windows.net/container]
WITH IDENTITY = 'SHARED ACCESS SIGNATURE',
SECRET = '<YourSASToken>';
  • Enable backup compression to reduce the estimated backup footprint before it hits the endpoint:
EXEC sp_configure 'backup compression default', 1;
RECONFIGURE;

Step 4: Validate File Size Estimates Before Running Full Backup

  • Use a trial run with the WITH STATS and NO_COMPRESSION flags removed to get an accurate estimated backup size in the SQL Server error logs or messages tab.
  • Compare this estimate against your endpoint’s documented size limit (1 TB for Page Blob, up to 4.75 TB per block blob file in some configurations).
  • Adjust the number of striped files accordingly (e.g., divide total estimated size by 900 GB to determine stripe count with safety margin).

Alternative or Verification Steps

  • After reconfiguring, run RESTORE VERIFYONLY FROM URL = '<backup_url>' on each striped file to confirm the backup set is valid and was written successfully without truncation errors.
  • If the error persists, consider using SQL Server Managed Backup to Microsoft Azure or a local disk backup followed by a separate file transfer/upload utility (like AzCopy) to bypass the native backup-to-URL size estimation entirely.