STATUS_FILEMARK_DETECTED (0X8000001B): Tape Drive Filemark Fix

When This Error Hits

You'll usually see STATUS_FILEMARK_DETECTED (0X8000001B) during a tape backup or restore job. Maybe you're using Windows Backup, Symantec Backup Exec, or Veeam — it doesn't care which. The job stops dead with something like "A filemark was detected" and the tape drive logs a CHECK CONDITION status. I've seen it most often on LTO-5 and LTO-6 drives connected via SAS or Fibre Channel, especially when someone tries to read a tape that was written by a different drive or firmware version.

Root Cause in Plain English

Tape drives don't work like hard drives. They write data in blocks, separated by markers called filemarks. A filemark is like a bookmark in a book — it tells the drive where one file ends and the next begins. The problem is, some backup software and tape drives get confused when they hit a filemark unexpectedly. For example, you might be trying to overwrite a tape that has existing data. The drive sees a filemark, thinks you're trying to read past the end of valid data, and throws this error. Or you might be restoring a tape that was written in a different block size (like 64KB instead of 256KB), and the drive can't reconcile the filemarks.

Another common trigger: someone forgot to rewind the tape before starting a new job. The drive parks at the first filemark from the last write, and the new job doesn't know how to handle it. Had a client last month whose entire print queue died because of this — their backup software crashed, and they couldn't restore until we cleared the tape.

The Fix — Step by Step

1. Identify the Tape and Drive State

First, check if the tape has data on it. Run fsutil in an admin command prompt:

fsutil volume diskfree T:

Replace T: with your tape drive letter. If it shows 0 bytes free, the tape is full or has filemarks that need clearing. If it shows errors, you've got a hardware issue.

2. Rewind or Erase the Tape

In most cases, you just need to rewind the tape to the beginning. Use this command:

mt -f \\.\Tape0 rewind

Change Tape0 to your drive number (check Device Manager under Tape Drives). If that doesn't clear the error, erase the tape:

mt -f \\.\Tape0 erase

This will overwrite all filemarks and start fresh. Warning: This deletes everything on the tape.

3. Fix Block Size Mismatch

If you're still getting the error, the tape was written with a different block size. Most backup software lets you set block size in the device settings. For LTO-5, use 256KB blocks. For LTO-6, 256KB or 512KB works. Open your backup software's tape drive configuration and match the block size to what's on the tape. If you don't know the original block size, try 64KB, 128KB, 256KB, and 512KB until one works.

4. Update Drive Firmware

Go to the drive manufacturer's site (HP, IBM, Quantum) and download the latest firmware. Outdated firmware is a common cause of filemark errors across different tape generations. Flashing it usually takes a few minutes and doesn't need special hardware — just a SAS or Fibre Channel connection and the vendor's update tool.

5. Check the SAS/Fibre Channel Cable

Bad cables cause intermittent errors that look like filemark issues. Swap the SAS cable if you have one. Had a case where a loose SAS connector on an LTO-6 drive caused this exact error every 4th backup job. Cost me an hour to find.

Still Failing?

If the error persists after all that, you're looking at a hardware problem. Run a drive diagnostic — HP has a built-in test, IBM uses ibmtapeutil. If the test fails, the drive head is dirty or damaged. You can buy a cleaning tape (LTO cleaning cartridge) and run it through. If that doesn't fix it, the drive needs replacement. No software fix will save you then.

One last thing: check the tape itself. If it's physically damaged or has been dropped, the media might be toast. Try a different tape from the same batch. If the new tape works, toss the old one.