How to fix Error 315 on Windows Server 2025 / Windows 11

by

Troubleshooting Guide: SQL Server Error 315 — Disabled Index or Offline Filegroup

Why This Error Happens

This error occurs when a query references a table whose index has been explicitly disabled (via ALTER INDEX ... DISABLE) or when the index resides in a filegroup that is currently offline, restoring, or otherwise inaccessible. SQL Server 2025 cannot use the query optimizer’s chosen access path if the underlying index structure is unavailable, and unlike a missing table, it will not silently fall back to a table scan when an index is explicitly disabled. This is commonly triggered after a partial database restore, a filegroup failure, corrupted data files, or a maintenance script that disabled indexes for a bulk load and never re-enabled them.

Step-by-Step Resolution Guide

Step 1: Identify the Disabled Index or Offline Filegroup

  • Run the following query to check index status:
  • SELECT i.name AS IndexName, i.is_disabled, t.name AS TableName FROM sys.indexes i JOIN sys.tables t ON i.object_id = t.object_id WHERE i.is_disabled = 1;
  • Cross-reference the filegroup status using SELECT name, state_desc FROM sys.filegroups; or SELECT name, state_desc FROM sys.database_files;
  • Note whether the issue is a disabled index (logical) or an offline filegroup (physical/storage).

Step 2: Rebuild the Disabled Index (If Applicable)

  • If the index was disabled intentionally (e.g., before a bulk insert), rebuild it using:
  • ALTER INDEX [IndexName] ON [SchemaName].[TableName] REBUILD;
  • For all disabled indexes on a table at once, use ALTER INDEX ALL ON [TableName] REBUILD;
  • Confirm sufficient disk space exists on the drive hosting the data files, typically under C:\Program Files\Microsoft SQL Server\MSSQL17.MSSQLSERVER\MSSQL\DATA\ on Windows Server 2025/Windows 11 default installs.

Step 3: Bring the Filegroup Back Online

  • Check the physical file path status in SQL Server Configuration Manager or via sys.master_files.
  • If the filegroup is marked OFFLINE due to a missing or corrupted .ndf/.mdf file, verify the file exists at its expected path (e.g., D:\SQLData\SecondaryFG.ndf).
  • Restore the affected filegroup from the most recent backup using:
  • RESTORE DATABASE [YourDB] FILEGROUP = 'YourFileGroup' FROM DISK = 'D:\Backups\YourDB.bak' WITH RECOVERY;
  • If the underlying disk or storage volume was disconnected (common in Windows Server 2025 storage spaces configurations), reattach the volume via Disk Management first.

Step 4: Review SQL Server Error Logs and Event Viewer

  • Open Event Viewer on Windows Server 2025/Windows 11 and navigate to Applications and Services Logs > MSSQLSERVER.
  • Cross-reference Error 315 timestamps with any I/O or storage-related warnings (Error 823/824) that may indicate the root storage issue.
  • Check ERRORLOG located at C:\Program Files\Microsoft SQL Server\MSSQL17.MSSQLSERVER\MSSQL\Log\ERRORLOG for additional context on why the filegroup went offline.

Alternative or Verification Steps

  • Re-run the original query that triggered Error 315 and confirm it executes without the disabled index/filegroup message; also validate with DBCC CHECKDB('YourDB') WITH NO_INFOMSGS to confirm database integrity.
  • If rebuilding fails due to storage corruption, restore the entire database from the last known good full backup rather than attempting a filegroup-only recovery.