sid@linus.UUCP (Sid Stuart) (03/22/84)
I have a tu80 on a Vax 780, running 4.2bsd. When I use the dump program to dump a file system to tape, if the dump needs more than one tape, I get a write error near the end of the tape. When I tell dump that the tape is only 2200 feet long, everything works out fine. This indicates that the estimate of the interrecord gap the dump uses does not correspond to what the tu80 is using. I asked my dec repairman if he could change the interrecord gap on a tu80 and he did not know anything about it. My question is, do other people get a whole 2300 feet out of their tapes on tu80's? Can the interrecord gap on the tu80 be changed? sid@linus
obrien@Rand-Unix.ARPA (03/28/84)
TU80's are not the only drives with this problem. Our "dump" program (4.1) also overshot some of our tapes. I checked the code, and after some arithmetic and checking of specifications I decided that it was correct. So either the specs are wrong (cumulative error over 2400'), or some tapes just come short from the manufacturer. We use shell scripts to do dumps and I just added a flag to tell "dump" that the tape was about 2300' long, and everything works fine now. Our drive is a TU45. I think we just went ahead and did the same thing with our TU78 when we installed scripts for that system, so I don't know if things come up short over there or not. Anyway, it's a problem.
shannon@sun.uucp (Bill Shannon) (04/04/84)
TU80's use an IRG of 1.2". In 4.2 dump look for the constant 7 (.7") and change to 12 in dumpmain.c, dumptape.c, and dumprtape.c. You might want to do an mt ioctl call and set the IRG based on the tape type (close enough for DEC drives, not accurate for all emulations), or perhaps (yet another) option to dump. Bill Shannon Sun Microsystems, Inc.
swine@orac.UUCP (Peter Swain) (04/11/84)
One of our customers has reported similar problem with TU80s, 2200' being about the right figure for dump. My guess is that the transitions to/from screaming mode write extended gaps. From memory, the standard IRG is .5", but an EIRG of up to 6"(??) is defined for use in (say) skipping flakey tape patches by moving the blocks around past the grotty bits. Now I think about it, the Dump manual (or the code) admits the *assumption* of .5" gaps. peter swain Siromath