How to fix Error 7948 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: SQL Server Error 7948 (“Avg. Pages per Extent”)

Why This Error Happens

Error 7948 is generated by DBCC CHECKDB (or DBCC CHECKALLOC) as part of its informational output regarding space allocation, specifically reporting the “Avg. Pages per Extent” ratio for a database. While the message itself is typically just a statistical output rather than a critical failure, it is often reported alongside corruption warnings when the underlying extent allocation bitmaps (GAM, SGAM, or IAM pages) are damaged due to improper shutdowns or storage-level I/O failures. In Microsoft SQL Server 2025 running on Windows Server 2025/Windows 11, this usually surfaces when the storage subsystem has a mismatch between physical disk sector sizes and the SQL Server page allocation unit, or when a checkpoint process was interrupted by a hardware failure.

Step-by-Step Resolution Guide

Step 1: Isolate the Database and Check Immediate Integrity

  • Open SQL Server Management Studio (SSMS) and connect to the Windows Server 2025 instance.
  • Run the following command to check the full scope of the error without the server attempting repairs yet:
  DBCC CHECKDB ('YourDatabaseName') WITH NO_INFOMSGS, ALL_ERRORMSGS;
  • Look for accompanying error codes (e.g., Error 8909 or 8928) that usually trigger the 7948 statistical readout; isolate if this is a standalone stat or a symptom of a larger corruption event.

Step 2: Verify Windows Server Storage and Disk Health

  • Navigate to Server Manager > File and Storage Services > Disks to check the physical health status of the volume hosting the .mdf and .ldf files.
  • Open an elevated PowerShell terminal and run a check on the specific volume’s file system integrity:
  Repair-Volume -DriveLetter D -Scan
  • Confirm that the disk sector size configuration in Windows Server 2025 matches the SQL Server 2025 instance configuration (4K alignment is required for 2025 builds).

Step 3: Execute Targeted Repair (If Corruption is Confirmed)

  • If Step 1 confirmed allocation errors beyond the standard stat message, take the database into single-user mode via SSMS or a query window:
  ALTER DATABASE YourDatabaseName SET SINGLE_USER WITH ROLLBACK IMMEDIATE;
  • Run the repair command specific to allocation errors (use with caution as this may result in data loss):
  DBCC CHECKDB ('YourDatabaseName', REPAIR_ALLOW_DATA_LOSS);
  • Revert the database back to multi-user access once the repair job completes:
  ALTER DATABASE YourDatabaseName SET MULTI_USER;

Step 4: Restore From Backup (Preferred Method)

  • Navigate to your backup directory (commonly C:\Program Files\Microsoft SQL Server\MSSQL17.MSSQLSERVER\MSSQL\Backup\) to locate the latest clean .bak file.
  • Perform a standard restore operation to overwrite the corrupted extents entirely, ensuring minimal data loss compared to the REPAIR_ALLOW_DATA_LOSS flag.

Alternative or Verification Steps

  • Verify the Fix: Re-run DBCC CHECKDB ('YourDatabaseName') WITH NO_INFOMSGS; and confirm the command returns “0 allocation errors and 0 consistency errors.”
  • Alternative Solution: If the error persists after a repair, detach the database, move the physical files to a different, verified-healthy disk volume on the Windows Server 2025 host, and re-attach it via CREATE DATABASE...FOR ATTACH.