How to fix Error 909 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: Error 909 – Data Compression / Vardecimal Storage Edition Mismatch

Why This Error Happens

This error occurs when a database containing objects configured with data compression (row or page compression) or the legacy vardecimal storage format is attached to, restored on, or started by an edition of SQL Server 2025 that does not support these Enterprise-tier features. SQL Server performs a compatibility check during database startup, and if it detects these storage attributes on a non-Enterprise edition (such as Standard, Web, or Express), it refuses to bring the database online to prevent data access inconsistencies. This commonly happens after downgrading an edition, migrating a database to a lower-tier licensed server, or restoring a backup onto mismatched hardware/licensing.

Step-by-Step Resolution Guide

Step 1: Identify the Current SQL Server Edition

  • Open SQL Server Management Studio (SSMS) and connect to the instance.
  • Run the following query to check your current edition:
SELECT SERVERPROPERTY('Edition') AS Edition, SERVERPROPERTY('EngineEdition') AS EngineEdition;
  • If the result is not “Enterprise Edition” or “Developer Edition,” this confirms the root cause.

Step 2: Locate Objects Using Compression or Vardecimal Storage

  • Before attempting any fix, identify which tables/indexes are causing the conflict by querying the source server (if still accessible) or a compatible Enterprise instance:
SELECT OBJECT_NAME(object_id) AS TableName, 
       data_compression_desc 
FROM sys.partitions 
WHERE data_compression > 0;
  • Note down all affected table and index names for the next step.

Step 3: Remove Compression Settings on a Supported Instance

  • On an Enterprise or Developer edition instance where the database can start, run the following for each affected object to disable compression:
ALTER TABLE [YourTableName] REBUILD WITH (DATA_COMPRESSION = NONE);
  • For vardecimal storage format, disable it using:
EXEC sp_tableoption 'YourTableName', 'vardecimal storage format', 'OFF';
  • Repeat this for every object identified in Step 2.

Step 4: Re-attach or Restore the Database to the Target Edition

  • Take a fresh backup of the database after compression has been removed.
  • Copy the .bak file to your Windows Server 2025 / Windows 11 target machine.
  • Restore the database using SSMS or T-SQL:
RESTORE DATABASE [YourDatabase] 
FROM DISK = 'C:\Backups\YourDatabase.bak' 
WITH REPLACE;

Step 5: Upgrade Edition (If Compression Is Required)

  • If data compression is a business requirement, consider upgrading your SQL Server 2025 license to Enterprise or Developer edition instead of stripping compression.
  • Use the SQL Server Installation Center to perform an edition upgrade: Setup.exe /ACTION=EditionUpgrade.

Alternative or Verification Steps

  • Verify the fix by attempting to bring the database online again (ALTER DATABASE [YourDatabase] SET ONLINE;) and confirm Error 909 no longer appears in the SQL Server Error Log.
  • As a quick alternative check, run sys.dm_db_persisted_sku_features on the target instance to confirm no Enterprise-only features remain enabled before migration.