[comp.sys.dec] using a DAT tape backup unit with a decstation 3100

anthony@cit-vax.Caltech.Edu (Lawrence Anthony) (01/10/90)

we recently acquired a 1.3GB DAT tape backup unit from tristar technology
for our decstation 3100 running ultrix 3.1/uws 2.1.  the drive unit is
made by wangtek and uses the dec-approved DDS data format.  it is presently
being used as a plug-and-play device and emulates an exabyte, i.e.
scsi_devtab.devtype = TZxx in /sys/data/scsi_data.c.  so far i have been
able to use dump/restore and tar quite successfully except in the
following cases:

1. using "tar c" to create a tape archive on the DAT unit works fine.
however, i cannot seem to add files to the archive using the "tar r"
command, at least not reliably.  i frequently (though not always) obtain
the following error message during the read and/or write stage:

	tar: Directory checksum error, possible file name:

this is followed by some gibberish that does not look like a file name
but more like part of a file on the tape.

this error is reproducible with different tapes with the error
seeming to occur in exactly the same position on the tape (judging
by the gibberish that accompanies the checksum error message.
is this a known bug/limitation in using tar with the "r" option under
ultrix?  or is this related to the oft-mentioned even- versus odd-byte
disconnect problem with exabytes.

2. the command "dd if=/dev/rmt0h of=/dev/null" gives the following
error message when used on recently written dump tapes:

	read: No such device or address
	12+0 records in
	12+0 records out

using /dev/nrmt0h instead of /dev/rmt0h gave the identical error message.
this was done with a tape onto which i had just written a dump of my
root (/) and /usr filesystems.  i know that the files were written
correctly as i have been able to restore a random sampling of the files
on the tape using the restore command.  i like to use this command to
verify that there were no errors on my dump tape.  this procedure works
properly when using dump/restore with tk50 tapes.  similar error messages
were obtained with a recently written tar tape as well as with files
written using the command "cp filename /dev/rmt0h".  i can however read
back files from the tape using the "dd" command if the files were copied
to the tape using the "dd" command in the first place.


3. the command "mt status" under csh gave the following error message:

	DDS DAT tape drive, residual=0
	Segmentation fault

issuing the same command under the Bourne shell (sh) gave a slightly
different error message:

	DDS DAT tape drive, residual=0
	Memory fault

the above messages were obtained with a tape loaded into the DAT unit.
in contrast, most of the other mt commands that i have tried, such as
"mt rewind" and "mt -f /dev/nrmt0h fsf 1" seem to work okay.  using
"mt offline" even causes the tape to be rewound and ejected.

4. does anybody have any suggestions for using the DAT unit to back up
VMS systems over ethernet (either Decnet or TCP/IP) and to back up
Macintoshes over ethertalk/localtalk/ethernet?  (we have an appletalk-
to-ethernet bridge from Cayman Systems.)  specifically i would like
recommendations for software products and vendors.  would the vms-ultrix
connection software do the job for vms?

5. i don't suppose dec will be releasing ultrix 3.2/uws 3.2 on DAT tape?

any explanations/solutions would be greatly apprecitated.  please direct
followups to comp.unix.ultrix.  (i had mistakenly requested that followups
go to comp.sys.ultrix in an earlier cancelled posting.)

thanks in advance.

lawrence anthony

e-mail:	anthony@csvax.caltech.edu
phone:	(818) 356-4474
FAX:	(818) 795-1547