Data Recovery from DLT tapes

Common Problems

• A loud grinding noise when DLT tape is inserted and no data can be read.
• The restore process fails with a DLT tape I/O or read error.
• A "fluttering" noise as the drive attempts to read. Error light illuminates.
• The DLT will not unload and no data can be restored.
• DLT cartridge unloads but the tape is still wound within the drive.
• The DLT has little or no data on but used to contained a full system backup.

These are a some of the many symptoms you might experience when there are problems reading or writing data with a DLT cartridge

Loud "grinding" from DLT 7000/8000 drives during loading

When a DLT is loaded the drive attempts to read the coarse alignment information that is stored prior to load point at the physical beginning of the tape. DLTIV can be used for recording data in any from the DLT4000, DLT7000 and DLT8000 formats, the latter two using a completely different set of heads, so the drive needs to get the alignment information then follow on to find which format the data is recorded using.

The awful grinding noise is the head positioning mechanism being pushed to it farthest extreme and then re-positioned to re-try reading. The heads are mounted on a block which is positioned using a worm-screw, this is the mechanism that makes that terrible sound.

(DLT IV is also used in DLT1 and VS80 drives, and the format they record using does not store the alignment and format information at the start of the tape and the end result will be that the drive will not come ready).

If you witness that the drive is struggling to load the tape, and with the noise it makes it is difficult to not notice, then it is important to take action. It could be that the drive is failing, in which case retire or repair the drive, but if the tape is the problem then presume that the trouble could worsen, get the data restored asap and backed up on to a working tape. Failure to do this could leave you needing the services of a tape data recovery company.

Restore fails with a medium error or I/O error

Usually there will have been some periods of stop-start motion ("shoe-shining") rather than the usual steady tape motion with the occasional pause. This indicates that the drive has been unable to read data at a particular position along the tape and that its sequence of retries has not resolved the problem. The cause of this problem could be physical, some level of damage to the tape, or it could result from poor quality recording of a failure of the recording media at that position.

If the problem is physical, for example the tape has stretched, creased or crumpled, then repeated attempts to access data risk making the problem worse and make tape data recovery probably the only option. Where it is a only a recording failure it could be practicable to perform a selective file restore and, if you are lucky, this could avoid the area of damage and get you the files that you need.

A couple of notes of caution, the recording format used by DLT is "serpentine" so the data is recorded in multiple tracks running forwards then backwards along the tape multiple times. If the problem is caused by damage this it is certain to affect more then the width of one track and so you will keep running into the problem along each track. Also, if the problem results from a failure in the drive that made the recording then the chances are the recording is marginal in several places and more errors are likely.

Fluttering or flapping noises from within the drive

A "fluttering" or "flapping" sound whiles the tape the loading might well be a sign that the leader strip within the drive has become detached. If this is the case then the drive unload light will be on and you will be able to eject the tape. The drive will have to be dismantled and the leader replaced or re-attached.

Such a sound during tape motion once the tape has been picked up by the leader, if accompanied by repositioning sounds (shoe-shining - backwards and forwards) indicates that an area of damaged tape is passing repeatedly across the read/write heads. Unfortunately the drive will go into its cycle of retries and will not stop until it finally gives up and reports a tape read error, and it might snap or further damage the tape during this time. The only way to stop it sooner is to power off the drive, then switch it on and it will take the tape to load-point - this too could damage the tape. It might be practicable to perform a selective restore of a vital file or two but this is a risky process. The serpentine pattern of DLT recording means that the damaged area of tape will be re-visited several times and the chances are the problem will be made worse. We advise getting assistance from a professional tape recovery company.

DLT Cartridge will not unload from the drive

If the tape has snapped within the drive then it will not be able to rewind and update its system areas, the tape will not then unload. There should be a whole array of flashing lights on the front of the drive indicating that something catastrophic has happened, and no sound of tape motion.

If you can hear the tape re-positioning, and periodically there is a "graunching sound" then the tape is intact but the drive is failing to read and update data prior to unloading. The problem could be with the drive or with the tape. You may be able to get the tape to unload by pressing the unload button and holding it in, if not then professional assistance will be needed if you need to recover the data.

Tape remains wound within the drive mechanism

The DLT tape sensing mechanism in the drive has failed and believes that the tape has mechanically unloaded. Do not pull the tape from the drive unless you really do not want the data back. You will quite quickly render it unrecoverable and will leave the drive leader incorrectly positioned.

Switch the drive off then insert the cartridge back into the drive enough to prevent further damage, then seek professional assistance. If a recovery is to be made then the drive will have to be sent with the tape still inserted so that the media can be extracted without further damage.

If you have removed the tape, and probably have a pile of tape on the floor, a recovery might still be practicable though rebuilding a partially working tape from a plastic bag full of unwound DLT media is a lengthy and expensive task. Get the drive repaired or replaced before trying another tape in it, we have seen cases where several valuable backups have been badly damaged before someone was finally convinced that a drive repair was probably a good idea.

DLT blank or reports no data as being stored

The DLT has probably been re-initialised (re-labelled), or the backup you want to restore has been overwritten. Specialist data recovery techniques will be required to recover the data.