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TK50 data recovery, look out for media degradation

TK50 was a major player in tape backup on VAX/VMS systems several years ago. Being fundamentally ½” (half inch) tape of the type used in open reel drives, but housed as DLT style cartridge, it suffers from the same long term storage problems as some brands of 1/2″ media. TK50 drives could store 70MB of data, and took quite a long time to fill, so have long since ceased to be a viable backup option even if you can find drives and media. But, there are a surprising number of tapes out there with data on them and recent weeks seem to have brought forth a flurry of requests to get data from them, and in one case to copy some. In a high proportion of these cases the data transfer operation has ended up being a data recovery exercise involving considerable work in the lab.

It might seem an odd request, to copy tapes that went out with the ark, but if you have a dedicated system based around a VAX workstation (for example some CAM systems used VAX) you might still be using it or have a request for design information from a couple of decades ago. VAX systems were well built so will often be in good working order, but if the method of booting is from TK50 tape then the problems can begin.

One of the biggest problems we see with TK50 tapes in our tape data recovery lab is “stiction”, the tape sticks to the read/write head. This is a result of media decay, the material bonded within the media to keep it sliding over the heads smoothly breaks down and suddenly the tape that was running nice and quickly comes to an abrupt halt. Worse still, there is some momentum involved and the dragging of the tape over the heads whilst waiting for it to stop moving can leave a lot of the recorded surface as a gooey mess on the heads. The result, a nice bit of see-through tape and data that will never been seen again.

Is all lost when the media decays in this manner? Not always, in our data recovery lab we have developed methods for keeping the tape moving and stopping it sticking. Usually this allows a recovery of the majority of the data from tape, though we often only get hold of a tape after several failed attempts have already been made and there are already some holes in the media.

The thing to consider if you do have data stored on TK50, TK70 or half-inch open reel tape is that it could be suffering from decay, this could be getting worse, and if there is a likelihood that data will be needed at some time in the future it is worth weighing up the cost of a data migration project now against the cost of a data recovery exercise some time hence.

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