raj@pollux.geog.ucsb.edu (Richard A Johnson) (05/25/91)
HELP! I need help from anyone out there who has dealt with 8mm video tape
drives a lot! Here's the problem:
I backed up this person's files on 8mm video tape (just the /u files that is).
Then I totally reinstalled their system from scratch bring it up to the latest
rev. later (3005 - but it's not really relevant). I then proceeded to restore
their files. That's when I found that the tape had a bad spot! If you
manually advance the tape a little you find a place where it's crinkled a
little bit. When the drive gets to that part it stops reading and returns
an error ("The media surface is damaged").
Eventhough "restore" says it's "Ignoring data and continuing", it doesn't get
anywhere because the drive simply can't track past that bad part!
I have tried the obvious:
1) tctl -f/dev/rmt0.1 fsr somenumber
(where "somenumber" has been anything from 1 to 500)
It doesn't skip past the bad point
2) tctl -f/dev/rmt0.1 fsf somenumber
Still doesn't skip past the bad part.
I could manually forward the tape past the bad part but when you put it into
the drive the first thing the drive does is rewind it! I can't find any
IOCTL, etc. which will tell the drive not to rewind the tape. Maybe there's
a dip switch on the drive itself?
The ONLY thing I can think of would be to take the tape apart, cut off the bad
part at the beginning, reattach the rest to the tapeup spool, and use dd to
read the data straight into a file. Then write a program to read the
restore file (IBM says there isn't any documentation on the format of the
file!) and get as much as possible back. I'm not completely sure this would
work since I bet the drive writes checksum information onto the tape and when
you try to get it to start in the middle of it, it's not going to like it
at all.
The reason why I figure the drive writes extra info on the tape is that
otherwise how would it know that the "media surface is damaged"? If this
isn't how it tells, then there may be hope for flattening the tape out?
I don't have high hopes for that simply because while I've been writting this
I was trying to read some of my incremental saves. One tape in particular
read just fine the first 4 or so times and then started giving the same type
of problem! Now I doubt that the tape got mangled while it was still in the
drive! (Yea, I know, maybe it did. That would mean I have a bad drive and
all bets are off until I get it fixed. I don't think that's that big of a
chance really.)
Am I missing anything? Is there some way out of this? How do you read past
a bad part of an 8mm tape? It seems impossible! You can bet I'm going to
re-read ALL saves to 8mm tape in the future! (I know, I should have
this time...)
Many thanks for ANY help or ideas!
/rajherb@ajfcal.uucp (Herb Peyerl) (05/26/91)
raj@pollux.geog.ucsb.edu (Richard A Johnson) writes: >their files. That's when I found that the tape had a bad spot! If you >manually advance the tape a little you find a place where it's crinkled a >little bit. When the drive gets to that part it stops reading and returns >an error ("The media surface is damaged"). When was the last time you cleaned this drive??? I once had a drive totally mangle a tape beyond repair, that's when I learnt to clean the drive about every 30 hours of use... Haven't had a problem since then... We've been using exabyte drives since '87 to back up our Apollo network... We use 4 of them every night and back up about 1.6 GB on each. Also, ever since we switched from the Sony VIDEO tapes to the actual REAL Exabyte tapes, we've never had another soft media failure... With the sony's, we were getting about 1 bad tape every month... >IOCTL, etc. which will tell the drive not to rewind the tape. Maybe there's >a dip switch on the drive itself? I know there isn't one on the drives WE get which are manufactured by Exabyte.... It's likely your drives are manufactured by the same company. >The ONLY thing I can think of would be to take the tape apart, cut off the bad >part at the beginning, reattach the rest to the tapeup spool, and use dd to I've never tried this so I can only speculate that it won't work... The data is written onto the tape in much the same way as video information is written to the tape... ie: ------------------------ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ------------------------ So, I'm fairly certain that if you cut a chunk out, the smarts in the Exabyte drive itself would still detect an error and rewind... >I was trying to read some of my incremental saves. One tape in particular >read just fine the first 4 or so times and then started giving the same type >of problem! Now I doubt that the tape got mangled while it was still in the It's happened to me, I don't doubt it's just happened to you. 'Specially if you haven't cleaned it... I'm not an expert, but 4 drives for 4 years adds up to a fair chunk of experience. Buy the 12 cycle cleaning kits from Exabyte. I know all their stuff is expensive, but how much is your data worth anyways? >a bad part of an 8mm tape? It seems impossible! You can bet I'm going to >re-read ALL saves to 8mm tape in the future! (I know, I should have >this time...) I've never lost ANY data by re-reading the data I knew I was about to destroy... Sometimes a second copy is not entirely out of the question. Also, reading all the backup logs every morning helps out. -- -------------------------------------------------------------------------- UUCP: herb@ajfcal.UUCP || #define Janitor Administrator I brew, therefore I am.. || Apollo System_Janitor, Novatel Communications "I spilled spot remover on my dog and now he's gone..." <Steven Wright>
raj@pollux.geog.ucsb.edu (Richard A Johnson) (05/31/91)
raj@pollux.geog.ucsb.edu (Richard A Johnson) writes: Remember this message? >HELP! I need help from anyone out there who has dealt with 8mm video tape >drives a lot! Here's the problem: >I backed up this person's files on 8mm video tape (just the /u files that is). >Then I totally reinstalled their system from scratch bring it up to the latest >rev. later (3005 - but it's not really relevant). I then proceeded to restore >their files. That's when I found that the tape had a bad spot! If you >manually advance the tape a little you find a place where it's crinkled a >little bit. When the drive gets to that part it stops reading and returns >an error ("The media surface is damaged"). >Eventhough "restore" says it's "Ignoring data and continuing", it doesn't get >anywhere because the drive simply can't track past that bad part! Well, here's the answer! I hope it helps someone else sometime. If you simply run the restore as normal and let it keep printing the error message about "Ignoring data and continuing" over and over and over... (It takes on the ordr ot 6 hours so just let it run forever!) it WILL finally get past that part and retrieve the rest of the data! Strange but true! Probably it advances the tape a very little bit every time the read call is issued so you just have to let it try and try and try... I talked to the IBM person who got me this answer and we agreed that the IBM documentation people should think seriously about adding something somewhere in their documentation saying that this is possible. ----------------------------------------------------------------------------- Richard A. Johnson raj@ncgia.ucsb.edu (Internet) NCGIA Computing Resources Manager ucbvax!ucivax!raj (UUCP) U. C. Santa Barbara raj@VOODOO (via BITNET)