stanonik@nprdc.navy.mil (Ron Stanonik) (08/24/89)
We recently attached an exabyte to a sun4/280 running sunos4.0.1. While becoming familiar with the exabyte, we ran into some quirks of scsi tape handling; ie, the archive tape drive behaves the same. 1) The non-rewinding device seems to rewind if you close before reading the filemark. For example, make a tape contain one file, two blocks long dd if=/etc/termcap of=/dev/rst0 count=2 Now try reading the tape one block, at a time dd if=/dev/nrst0 count=1 dd if=/dev/nrst0 count=1 Both dd's returned the same (first) block. 2) You cannot read data past a filemark, unless you first read the filemark and close. For example, make a tape containing two files dd if=/etc/termcap of=/dev/nrst0 count=1 dd if=/etc/format.dat of=/dev/nrst0 count=1 Now read several blocks without closing. For this you need a little program that opens /dev/nrst0 and does several read's. The first read returns the termcap block, but successive reads only return 0. On the other hand dd if=/dev/nrst0 dd if=/dev/nrst0 will read first the termcap, then the format.dat. Maybe this all is according to scsi tape semantics (if there is such a time)? I'm not familiar enough with scsi to say whether this is correct or not. 1/2" drives on our vax (4.3bsd) and suns (xt, not scsi) behave differently. That is, the non-rewinding device doesn't rewind, and reads will read past a filemark. That's what I would expect. Ron Stanonik stanonik@nprdc.navy.mil