How to fix Error 9026 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: SQL Server Error 9026 – Consolidated Log IO Failure

Why This Error Happens

Error 9026 occurs when SQL Server 2025 encounters an I/O failure while writing to or reading from the consolidated transaction log in a multi-tenant host database architecture. This is typically caused by underlying disk subsystem issues, storage controller timeouts, or file-level corruption affecting the log file associated with a specific tenant. It can also surface when the storage path has intermittent connectivity (common with SAN/NAS or cloud-attached storage like Azure Disk) or when antivirus/filter drivers interfere with log file handles on Windows Server 2025.

Step-by-Step Resolution Guide

Step 1: Verify Disk and Storage Health

  • Open Event Viewer on Windows Server 2025 and check the System log for Disk or Storport warnings (Event ID 153, 129, or 51) around the same timestamp as Error 9026.
  • Run chkdsk <DriveLetter>: /f /r on the volume hosting the log files to detect and repair file system errors.
  • If using virtualized or SAN storage, confirm there were no recent failover, latency spikes, or firmware updates on the storage controller.

Step 2: Check SQL Server Log File Location and Permissions

  • Open SQL Server Configuration Manager and confirm the SQL Server service account has Full Control permissions on the folder containing the consolidated log file (commonly under D:\SQLData\Logs\ or the tenant-specific log directory).
  • Validate there is no file lock conflict by checking if third-party backup or antivirus software has an active handle on the .ldf file using Resource Monitor (Disk tab → search for the log file name).
  • Exclude the SQL Server data and log directories from real-time antivirus scanning via Windows Defender or your endpoint protection console.

Step 3: Run DBCC CHECKDB on the Host Database

  • Connect via SQL Server Management Studio (SSMS) and run:
  DBCC CHECKDB (N'HostDatabaseName') WITH NO_INFOMSGS, ALL_ERRORMSGS;
  • Review output for log corruption or allocation errors tied to the reported tenant ID.
  • If corruption is confirmed, restore the affected tenant’s log segment from the most recent verified backup rather than attempting a repair that could cause data loss.

Step 4: Increase I/O Timeout and Review SQL Server Error Log

  • Navigate to C:\Program Files\Microsoft SQL Server\MSSQL17.MSSQLSERVER\MSSQL\Log\ERRORLOG and look for preceding I/O-related warnings (e.g., “I/O requests taking longer than 15 seconds”).
  • If timeouts are frequent, work with your storage administrator to increase the Disk I/O Timeout value in the registry key:
  HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Disk\TimeOutValue
  • Set the value to 60 (decimal) if currently lower, then restart the server to apply changes.

Alternative or Verification Steps

  • After applying fixes, force a tenant-specific log flush with CHECKPOINT; followed by DBCC SHRINKFILE (if safe) and confirm no new 9026 errors appear in the SQL Server Error Log over a 24-hour monitoring window.
  • If the issue persists, failover to a secondary replica (if using Always On Availability Groups) and perform a full consistency check on the primary before reintroducing it to the cluster.