How to fix Error 4202 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: Error 4202 – BACKUP LOG Failure Due to Bulk Logged Changes and Unavailable Filegroups

Why This Error Happens

This error occurs because the database uses the Bulk-Logged recovery model and minimally logged operations (such as BULK INSERT, SELECT INTO, or index rebuilds) have modified extents on a filegroup that is currently offline, corrupted, or otherwise inaccessible. SQL Server 2025 requires read access to every data extent touched by bulk-logged operations when backing up the transaction log, because the log backup must capture the actual data pages rather than just log records. If even one filegroup containing bulk-logged changes cannot be read, the entire log backup operation is blocked to prevent an inconsistent or unrecoverable backup chain.

Step-by-Step Resolution Guide

Step 1: Identify the Unavailable Filegroup

  • Run the following query to check filegroup and file status:
  • SELECT name, state_desc, physical_name FROM sys.master_files WHERE database_id = DB_ID('YourDatabaseName');
  • Look for any file with a state_desc value other than ONLINE (e.g., OFFLINE, RECOVERY_PENDING, or SUSPECT).
  • Cross-reference the physical file path to confirm it exists on disk at the expected location (e.g., D:\SQLData\YourDB_FG2.ndf).

Step 2: Restore or Reconnect the Missing File

  • If the underlying disk or volume was disconnected, reattach the storage in Windows Server 2025 Disk Management and verify drive letter consistency.
  • If the file is corrupted or missing, restore it from the most recent full or differential backup using:
  • RESTORE DATABASE YourDatabaseName FILE = 'YourDB_FG2' FROM DISK = 'E:\Backups\YourDB_Full.bak' WITH NORECOVERY;
  • Apply any subsequent differential or log backups in sequence to bring the filegroup back online.

Step 3: Bring the Filegroup Back Online

  • Once files are restored, run ALTER DATABASE YourDatabaseName SET ONLINE; if the entire database was marked offline.
  • For a single filegroup, use ALTER DATABASE YourDatabaseName MODIFY FILEGROUP YourDB_FG2 ONLINE; if supported for your edition.
  • Confirm the filegroup state has changed by re-running the sys.master_files query from Step 1.

Step 4: Switch to FULL Recovery Model (If Bulk-Logged Is Not Required)

  • Open SQL Server Management Studio (SSMS) and right-click the database, then select Properties > Options.
  • Change the Recovery Model from “Bulk-logged” to “Full” to prevent future occurrences tied to minimally logged operations.
  • Alternatively, run: ALTER DATABASE YourDatabaseName SET RECOVERY FULL;

Step 5: Retry the Log Backup

  • Execute the log backup command once all filegroups report ONLINE:
  • BACKUP LOG YourDatabaseName TO DISK = 'E:\Backups\YourDB_Log.trn';
  • Confirm the backup completes without raising Error 4202 again.

Alternative or Verification Steps

  • Verify success by querying sys.databases and confirming log_reuse_wait_desc no longer shows LOG_BACKUP and the database state is ONLINE for all files.
  • If the filegroup cannot be recovered (e.g., permanent hardware failure), take a full database backup immediately after switching to the Full recovery model, since the broken log chain will require a fresh backup baseline before log backups can resume.