01-23-2016
Lots of questions to ask about this.
Do you know for certain that it's a tar tape and not cpio or some other proprietary format?
Sometimes tape formats have a header so use a no rewind 'nr' device to prevent rewinding, stopping the tape where it is, and then try again.
Do you know the blocking factor the tape was written in?
If you're trying to read it raw with dd, trying appending each of bs=512, bs=1024, bs=2048 and bs=4096 to the dd command. Perhaps tar was configured to write a different block factor to what dd is defaulted.
DAT's always know internally (without reference to the O/S) if they are reading junk. The DAT mechanism writes enough checksums (created by the drive) to know when the integrity of the data is compromised.
---------- Post updated at 01:57 PM ---------- Previous update was at 11:57 AM ----------
Other thoughts are:-
also try bs=10240 in case it's written with the commonly used block size of 10k
Was the tape written by this DAT drive? Tape transports can go out of alignment (the posts that guide the tape) so you may well find that if you put the tape into the drive that wrote it, it will read with no problem.
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TM(4) Kernel Interfaces Manual TM(4)
NAME
tm - TM-11/TE-10 magtape interface
SYNOPSIS
/sys/conf/SYSTEM:
# Setting AVIVTM configures the TM driver for the AVIV 800/1600/6250
# controller. For more details, see /sys/pdpuba/tm.c.
NTM tm_drives # TM11
AVIVTM YES # AVIV 800/1600/6250 controller
/etc/dtab:
#Name Unit# Addr Vector Br Handler(s) # Comments
tm ? 172520 224 5 tmintr # tm11 driver
major device number(s):
raw: 7
block: 1
minor device encoding:
bits 0003 specify TS drive
bit 0004 specifies no-rewind operation
bits 0030 specify recording density:
0000: 800BPI
0010: 1600BPI (AVIVTM and some other controllers)
0020: 6250BPI (AVIVTM only)
DESCRIPTION
The tm-11/te-10 combination provides a standard tape drive interface as described in mtio(4). The standard DEC tm-11 operates only at 800
bpi. Other controllers of this type may also allow operation at 1600 bpi, under software control or by switching manually.
FILES
/dev/MAKEDEV script to create special files
/dev/MAKEDEV.local script to localize special files
SEE ALSO
mt(1), tar(1), tp(1), mtio(4), ht(4), ts(4), mt(4), dtab(5), autoconfig(8)
DIAGNOSTICS
te%d: no write ring. An attempt was made to write on the tape drive when no write ring was present; this message is written on the termi-
nal of the user who tried to access the tape.
te%d: not online. An attempt was made to access the tape while it was offline; this message is written on the terminal of the user who
tried to access the tape.
te%d: can't change density in mid-tape. An attempt was made to write on a tape at a different density than is already recorded on the
tape. This message is written on the terminal of the user who tried to switch the density.
te%d: hard error bn%d er=%b. A tape error occurred at block bn; the tm error register is printed in octal with the bits symbolically
decoded. Any error is fatal on non-raw tape; when possible the driver will have retried the operation which failed several times before
reporting the error.
te%d: lost interrupt. A tape operation did not complete within a reasonable time, most likely because the tape was taken off-line during
rewind or lost vacuum. The controller should, but does not, give an interrupt in these cases. The device will be made available again
after this message, but any current open reference to the device will return an error as the operation in progress aborts.
BUGS
If any non-data error is encountered on non-raw tape, it refuses to do anything more until closed.
3rd Berkeley Distribution January 28, 1988 TM(4)