SQL Server Log Filled the Disk

First, separate the storage problem from the database problem

Windows only tells you that the drive is full. The cause might be an LDF transaction log, an MDF or NDF data file, a backup written to the wrong volume, or something unrelated to SQL Server. Guessing at this point is risky.

Scan the affected drive in SizeTrend and open the Overview pane. Look for SQL Server database files. SizeTrend checks storage locations registered to local SQL Server instances and lists the MDF, NDF, and LDF files it finds there. The largest file usually becomes obvious very quickly.

What the instance name does and does not prove

SizeTrend can group a storage location under a local SQL Server instance when the registration points there. This is useful evidence, but it is based on the path. SizeTrend does not connect to SQL Server or inspect the databases themselves.

A detached database copy can still sit in a registered folder. Two instances can also share a storage location, while a database in a custom location may not appear in the expected group. Treat the instance label as a lead, then confirm the file in SQL Server Management Studio or your normal administration tools.

If the LDF file is the one that grew

A large transaction log is a result, not a diagnosis. Common causes include a missing log-backup chain, a long-running transaction, replication or availability work, and an operation that legitimately generated a great deal of log activity. The right response depends on the database recovery model and why the log cannot reuse space.

Check the database status, log backups, active transactions, and available disk space with SQL Server tools. If the database belongs to another team or application, bring them the exact filename, size, drive, and instance hint from the scan. That is far more useful than simply reporting that C: is full.

Never delete the database file in Explorer

Do not delete, rename, move, compress, or blindly shrink an MDF, NDF, or LDF file because it is large. Those files are live database storage, not disposable logs in the ordinary Windows sense. An emergency cleanup that damages the database is worse than the original low-space alert.

If another safe location on the drive is consuming space, you may be able to recover enough room there while the database problem is investigated. After the incident, scheduled SizeTrend scans can help show when the growth began and whether it is repeating.