An increasing number of local library systems are being configured with 8-mm helical scan tape drives. Not only are these less expensive than nine-track, open reel tape drives, but their tape capacity is also much greater, making it possible to back up an entire data base without changing tapes. These tapes, when purchased from vendors, usually cost $25-$30 each for a 2.2 GB tape. But local video stores sell 8-mm tapes which will work in the drives for $7 or less. Why such a difference? The tapes are not the same. Video grade tapes are cut from stock which is a meter wide and a thousand meters long. The process used to cut the tape into thin strips generates edge debris, which is subsequently deposited on the tape heads during the first several passes of a tape. Such a build-up eventually will result in reliability and performance problems. The more costly data grade tape has had the excess debris removed. Other differences for most data grade tapes are (1) the cases are tougher, (2) the tape coating is designed to be more uniform and flake-resistant, and (3) the tape is tested for dropouts and defects.
The risk with using other than data grade tape is not the likelihood of errors in the data, but tape drive reliability and performance. There are error correction techniques to check the tape, whether video or data grade, and if a defect is found, the block is written again. However, as the number of errors increases, the number of blocks to be rewritten increases and the time required for the back-up grow. If enough debris builds up on the heads, the tape drive may stop.
Even with data grade tape it is a good idea to clean the heads after every 30 hours of tape drive operation. Less frequent cleanings do not remove an excessive build-up of debris.
