How to fix Error 3260 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: SQL Server Error 3260 — “An Internal Buffer Has Become Full”

Why This Error Happens

Error 3260 typically occurs during BACKUP or RESTORE operations when SQL Server’s internal message buffer, used to format output strings (such as file paths or device names), exceeds its allocated size limit. This is most commonly triggered by excessively long file paths, overly verbose backup device names, or an accumulation of long error strings being concatenated into a single buffer during logging. In rare cases, it can also surface due to corrupted metadata in the backup history tables (msdb.dbo.backupset, backupfile) that causes malformed string generation.

Step-by-Step Resolution Guide

Step 1: Shorten File Paths and Device Names

  • Check the full path of your backup/restore target; Windows Server 2025 and SQL Server 2025 still respect legacy buffer limits even though NTFS supports long paths.
  • Move backup destinations to a shorter root path, e.g., from D:\SQLData\ProductionBackups\2025\DailyFull\ to D:\Backups\.
  • Avoid deeply nested UNC paths like \\FileServer01\SQLBackups\Department\Finance\2025\Q4\; shorten to \\FileServer01\Backups\.

Step 2: Clear and Rebuild Backup History Metadata

  • Open SQL Server Management Studio (SSMS) and connect to the instance via a new query window.
  • Run EXEC msdb.dbo.sp_delete_backuphistory @oldest_date = '2024-01-01'; to purge outdated backup history entries that may be corrupted or bloated.
  • Restart the SQL Server service via services.msc or run Restart-Service -Name 'MSSQLSERVER' in an elevated PowerShell session on Windows Server 2025.

Step 3: Split Backup Operations Across Multiple Smaller Devices

  • Instead of a single large backup command with many device files listed, break the BACKUP DATABASE statement into fewer striped files with shorter names.
  • Example: Replace BACKUP DATABASE MyDB TO DISK = 'D:\VeryLongDescriptiveBackupFileNameForMyDatabase.bak' with BACKUP DATABASE MyDB TO DISK = 'D:\MyDB.bak'.
  • Avoid using excessive WITH clause options in a single statement that generate long internal message strings (e.g., combining NAME, DESCRIPTION, and MEDIANAME with long text values).

Step 4: Apply Latest Cumulative Update for SQL Server 2025

  • Check the current build version using SELECT @@VERSION; in SSMS.
  • Download and install the latest Cumulative Update (CU) from the Microsoft Update Catalog, as buffer-handling bugs are frequently patched in CUs.
  • Reboot the Windows Server 2025 host after installation to ensure all binaries are correctly refreshed.

Alternative or Verification Steps

  • Re-run the original BACKUP/RESTORE command with shortened paths and names; confirm it completes successfully without raising Error 3260 in the SQL Server Error Log (Management > SQL Server Logs in SSMS).
  • If the error persists, enable Trace Flag 3014 (verbose backup logging) temporarily via DBCC TRACEON (3014, -1); to capture more granular diagnostic output and identify the exact string causing the buffer overflow.