How to fix Error 875 on Windows Server 2025 / Windows 11

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Why This Error Happens

Error 875 is not actually a failure—it is an informational message logged by the SQL Server Database Engine confirming that the Resilient Buffer Pool Extension (a persisted memory-mapped cache feature introduced to protect buffer pool data across restarts) has initialized correctly on the specified file. It typically appears in the SQL Server Error Log whenever the instance starts, restarts, or recovers from an unexpected shutdown, and the extension file is successfully remapped to its configured size. Users often mistake this for a critical error because it carries an “Error” severity classification in the log viewer, even though it indicates a successful operation, not a malfunction.

Step-by-Step Resolution Guide

Step 1: Confirm the Message Severity in SQL Server Logs

  • Open SQL Server Management Studio (SSMS) and navigate to Management > SQL Server Logs.
  • Locate the Error 875 entry and confirm the message text reads “…has been started successfully…”.
  • Cross-reference the timestamp with a recent service restart, failover, or Windows Server 2025 patch cycle to confirm it is a startup artifact, not an ongoing fault.

Step 2: Validate Buffer Pool Extension Configuration

  • Run the following T-SQL query to inspect current buffer pool extension settings:
SELECT * FROM sys.dm_os_buffer_pool_extension_configuration;
  • Check the path, file_size_in_kb, and state_description columns to ensure the extension file (commonly a .bpe file) resides on a fast SSD/NVMe volume as required by SQL Server 2025 resiliency features.
  • Verify the configured size aligns with your intended RAM-to-extension ratio (commonly 4x–10x physical RAM for OLTP workloads).

Step 3: Check File System Permissions and Disk Health on Windows Server 2025

  • Ensure the SQL Server service account has Full Control NTFS permissions on the folder containing the .bpe file (e.g., D:\SQLExtension\).
  • Open Event Viewer > Windows Logs > System and look for disk-related warnings (Event ID 153 or 157) that could indicate underlying storage latency affecting the extension remap process.
  • Confirm Storage Spaces Direct or local disk health using:
Get-PhysicalDisk | Select FriendlyName, HealthStatus, OperationalStatus

Step 4: Re-enable or Resize the Buffer Pool Extension (If Needed)

  • If the extension file was deleted or corrupted during an unclean shutdown, disable and re-enable it:
ALTER SERVER CONFIGURATION SET BUFFER POOL EXTENSION OFF;
ALTER SERVER CONFIGURATION SET BUFFER POOL EXTENSION ON
(FILENAME = 'D:\SQLExtension\BPE_Cache.bpe', SIZE = 50 GB);
  • Restart the SQL Server service via SQL Server Configuration Manager to confirm clean reinitialization.

Alternative or Verification Steps

  • Re-check the SQL Server Error Log after the next restart — a single, clean “started successfully” message with no accompanying warning (Error 876 or 878) confirms normal operation.
  • If the message repeats excessively on every short interval (not tied to restarts), run DBCC CHECKDB and inspect the storage subsystem for intermittent I/O failures, as recurring re-initialization may indicate disk instability rather than a logging quirk.