This is Exebyte-tape-drives+gnutar in view mode; [Up]
Date: Sun 07-Oct-1991 16:21:41 From: sherwood@space.ualberta.ca (Sherwood Botsford) Subject: Exebyte tape drives & gnutar I am having problems using a Dilog - Exebyte 8mm tape drive with our nexts. I am running a series of tar operations using gnutar. Sometimes, everything works like a charm. More often I am getting tape I/O errors at odd intervals. Scenario 1. First 15 files archive properly. Thereafter gnutar returns an I/O error while the tape positioning mechanism goes snake. Putting a sleep 10 between invocations of gnutar helps. Scenario 2. The first file on the tape is a very short file that I use as a label. (Actually: touch Friday-FullUserBack gnutar -cf /dev/nrxt0 Friday-FullUserBack ) This allows my scripts later to do things like set tapelabel = `gnutar -tf /dev/nrxt0` This works. However, under certain failure modes, this file gets clobbered, and I don't know why. I've tried using both the exebyte (nrxt0) and the general scsi tape (nst0) interfaces. Both fail, but not generally in the same way. I am wondering right now if it would work better to have the nrxt0 driver, but have fixed length blocks. Suggestions welcome. Answer here, or email.
Date: Sun 08-Oct-1991 22:28:13 From: sherwood@space.ualberta.ca (Sherwood Botsford) Subject: Re: Exebyte tape drives & gnutar Sherwood Botsford writes > > I am having problems using a Dilog - Exebyte 8mm tape drive with our nexts. > > I am running a series of tar operations using gnutar. Sometimes, everything > works like a charm. More often I am getting tape I/O errors at odd intervals. > > Scenario 1. > First 15 files archive properly. Thereafter gnutar returns an I/O error > while the tape positioning mechanism goes snake. Putting a sleep 10 > between invocations of gnutar helps. > > Scenario 2. > The first file on the tape is a very short file that I use as a label. > (Actually: > touch Friday-FullUserBack > gnutar -cf /dev/nrxt0 Friday-FullUserBack ) > > This allows my scripts later to do things like > set tapelabel = `gnutar -tf /dev/nrxt0` > This works. However, under certain failure modes, this file > gets clobbered, and I don't know why. > > I've tried using both the exebyte (nrxt0) and the general scsi tape (nst0) > interfaces. Both fail, but not generally in the same way. I am wondering > right > now if it would work better to have the nrxt0 driver, but have fixed length > blocks. Suggestions welcome. > Some answers to the situation: 1. gnutar 1.10 and my exebyte drive show the following behaviour. Maybe it is typical for exebytes. This works: Write a label rewind tape read label write tar files. This doesn't Write a label rewind tape read label write tar files rewind tape read a label write -- ! error -- Please insert volume 2. Several tests later it appears that I can write either at the end of media mark (two eofs in a row) or I can write from the beginning of the tape. It doesn't seem possible to read part way through a tape, then start writing. Is this behaviour designed into the exebyte because it is so poor at positioning the tape, or is it a fault of gnutar, or is it the fault of the mtio and scsi system calls. The answer for me was simple: Read the label, rewind the tape and rewrite the label. 2. Many of my problems with files getting clobbered were cured with a program called mtset, available in a file called scsitools.tar.Z. This allows me to set the tape driver for fixed blocks. 3. I was having problems getting my script to run from crontab. It turns out that Nexts are different from Risc 6000's in that the following will not work: 0 1 * * 1-4,7 command script. It turns out that you can have a time as either a range, or as a comma separated list, but not as both. Cron doesn't complain, it just ignores the line. This caused me no end of grief.
Date: Sun 08-Oct-1991 15:33:39 From: rich@vaxkiller.agi.org (Richard E. Showalter) Subject: Re: Exebyte tape drives & gnutar In article <1991Oct7.162141.5990@cs.UAlberta.CA> sherwood@space.ualberta.ca (Sherwood Botsford) writes: > > I am having problems using a Dilog - Exebyte 8mm tape drive with our nexts. > > I am running a series of tar operations using gnutar. Sometimes, everything > works like a charm. More often I am getting tape I/O errors at odd intervals. {stuff deleted) > Answer here, or email. > -- > => Sherwood Botsford sherwood@space.ualberta.ca <= > => University of Alberta Lab Manager, Space Physics Group <= > => tel:403 492-3713 fax: 403 492-4256 <= Have you tried to use different media in your Exebyte? I used to get all kinds of I/O errors using gnutar to backup to a WangDAT 1300 DAT drive, only to find out that the problems all went away when I switched to Sony DAT audio tape. This is not necessarily an endorsement for Sony, but the stuff works reliably for me.
Date: Sun 16-Oct-1991 20:38:29 From: louie@sayshell.umd.edu (Louis A. Mamakos) Subject: Re: Exebyte tape drives & gnutar This is just a guess, but on Exabyte 8mm tape drives, the drive can write a "short" EOF or a "long" EOF between tape files. I believe that the "short" EOF is such that you can read it as you go along, but you can't position from it, while a "long" EOF is such that you can position the tape to it and begin writing. There are two of them because a "long" EOF consumes a signifcant amount of space, on the order of a few 100KB (.5 or .75 inches?). Some SCSI tape drivers allow you to set which type of EOF they will write. I don't know about the NeXT's. louie
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