ghg@ei.ecn.purdue.edu (George Goble) (03/09/89)
****** Exabyte tape mangling warning - sequence to avoid --ghg 2/22/89. *** Stan Juday, ME dept computer site specialist here, was "playing around" with a drive we loaned the ME dept. This drive was outfitted with a clear plexi-glass cover. He filled up the tape and ran it off the end (on purpose), and got the expected hard error. He then did a backspace file command "mt bsf N" to back the tape up. To his horror, the tape began to get a little slack over Guide #7, and climbed part way off the guide, thus wrinkling it. The tape later returned to its normal position on the guide. Guide #7 is at the "10 o'clock" position. The drive was at firmware level MX4$23 / SV-B017 (servo). This is the first case of an Exabyte causing media damage since the summer of '87 (before it was a product) here. We even had an eye witness! I had executed the above sequence 2 or 3 times in the past, with no problems, but it was on older firmware revisions. The tape was a SONY P6-120MP, the standard 2hour (2GB) tape. More investigation revealed, that his drive tended to have the tape go slack around Guide #7 and the top Guide during a Backspace file operation (tape motion is reverse, at 10X read speed, drum tension on). The tape did not always come off the guide. As the backspace proceeded, the left reel (take up reel) increased in diameter, and the tape tension increased, so that at about the 3/4 point on the tape, the slack was not observed anymore. Seems to be some sort of servo problem. I mangled a 2nd tape, on another drive, at the 2/3 point into the tape, by initiating a bksp file operation. Exabyte (Jim Werder) has verified this problem to happen there also. I would imagine that new firmware will be tested there and here in the next few days. Until the servo code can be corrected, I would highly recommend that Backspace file/record (mt bsf or bsr) operations be prohibited, if positioned on the 2nd half of the tape. The special case of "mt bsf 1", being used to backspace over a filemark, can probably be allowed, since it only moves around 2", and should not let the slack conditon develope. Rewind/offline from the end of the tape, occurs with the drum under less tension, and does not cause the slack condition on Guide #7. Forward motion operations (read and file/record space forward) have no problems in this area. --ghg 2/25/89 George Goble, Engineering Computer Network, Purdue U, W. Lafayette IN 47907 (317) 494-3545 Arpa: ghg@purdue.edu uucp: {backbone}!pur-ee!ghg