Unable to read entire TK50 tape - Suggestions needed.

[Jan van den Ende]

Dan,

>>>
I just received a number of TK87 drives that I will test. But will wait until I attempt the TK70 drive. I just found a TK50 drive as well still wrapped in the packing envelope. I will try that as well.
<<<

Okay, but remember the SCSI vs DSA situation.

I have once read a 15 year old 800 BPI (!) tape
with just over 35000 (thirtyfive THOUSAND) recoverable errors. It took 0ver 4 hours, CPU bound (!), to recover a file that could be transfered to tape in about 3 minutes, but WE GOPT IT.
Multiple experience with TK50 & TK70 with > 100 recoverable errors.
A SCSI TK50 drive: ONE error is the end of it.
We held on to non-SCSI TK70 (and reel) drive drives just for such cases for many years. Definitely much slower, but we were more than ready to pay THAT price!

Ans it has already been remarkerd: clean the drive before AND AFTER each try!

Good luch (you will need some).

Proost.

Have one on me.

jpe

[Stanley F Quayle]

> I was a bit surprised that a power cycle did not effectively rewind the tape back into the cartridge.

This doesn't happen with TZ87's. At least, not on the six I have...

[Stanley F Quayle]

To clean those non-TZ87 tape drives, you'll need the DEC TKXX-HC cleaning kit. I found some listed on varx.com for $199...

[Bob Blunt]

Dan, I missed in your initial entry that the tape was stuck in the "can" so to speak. The behavior of the "brick" (the tape itself) in question depends on what the firmware has been programmed to do and there's firmware on several modules in one of those drives. The best solution, as previously mentioned, is to carefully use a powered screwdriver and rewind into the cartridge. You can (and I have, painfully) rewind using a regular screwdriver but it takes forever and your forearms will not quickly forgive you.

Leave the cartridge in the drive when you do this. My recommendation about opening the cartridge was intended just to check the tape itself for damage AFTER you have it rewound.

The power-on behavior with a partially unloaded cartridge can be strange. I've had some drives in that family that immediately sensed the tape and "promptly" wound it all onto the take-up reel inside the drive. This was usually when the MicroVAX got powered-off in a big hurry, the drive pulled and the screwdriver applied. Sometimes you can force the drive to rewind by mashing the unload button repeatedly (on the TK50/TK70 units). I haven't had great luck with the real DLT units but I also haven't had the frequency of problems I had with the original TK50s either. The old drives also had a wheel and sensor in a plastic housing that detected tape motion. Those would fill with a monster dust bunny and the sensor would fail and send the drive into weird mode. I rebuilt more than my fair share of TK drives back in the day just to get our operation back online. It can be frustrating.

bob

[abrsvc]

Update:

It would appear that the tape has some contamination on it. A slight "nudge" on the spindle released the tape and the unit was able to rewind the tape into the cartridge. The power cycle actually was attempting to move the tape, but was not able to because ofhte contamination. I don't have a clue what is on the tape that is causing this, but will investigate. I'll need to clean the tape somehow.

Stay tuned, as the saga is not yet complete...

Dan

[Stanley F Quayle]

You might search ITRC for more help, because this topic comes up from time to time.

As for cleaning the tape, there was once a non-DEC device that would clean TK50/TK70, but was discontinued years (>10) ago.

The usual problem isn't contamination of the tape, but the tape itself becomes sticky. There was an ITRC posting about baking the tape in a low-temperature oven to remove any moisture; the poster thought that humidity might be contributing to the stick problem.

[Bob Blunt]

Right, there was an issue with the cartridges being extremely sensitive to changes in humidity and temperature that resulted in a condition called "stiction" where the layers of wrapped tape would stick together. I think there was a Blitz that was released that cautioned about the situation and gave guidelines about how to handle it. There was a very small window of difference in humidity and temperature allowed.

There are companies who offer recovery services and address stiction issues on tapes they handle. Google returned several responses but I had to narrow down the search to find this: http://www.hp-store.com/PD_01382.aspx

I've never had a stiction problem on the early drives but that doesn't mean it wasn't happening and just not identified. I've always used the TK cleaner on the older TK50/70 and TZ30 drives and it can work some miracles. But if the media is peeled off the tape... ouch. I know that older reel-to-reel tapes could more easily fall-back on the redundancy groups for data recovery but the cartridge drives...especially DLT, DAT and 8mm in my experience...have to be specially coerced with recovery-capable firmware to even try. Hopefully with an older, non-SCSI TK drive you can get it to try harder.

bob